Author: Patrick Lutz

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Cementing is a well-established practice in the oil and gas industry. Its main purpose is to protect the wellbore from the surrounding downhole environment which includes prevention of unwanted communication of formation fluids with the wellbore or other permeable horizons. During a cement job the existing mud in the wellbore will be displaced by the spacer, to clean the pipe and borehole wall, followed by cement and a displacement fluid which usually is a mud. The intermixing between these fluids (spacer, cement, and mud) could arise during the placement phase which tends to affect the specified cement properties and hence jeopardize the quality of a cement job. Thus, a better understanding of intermixing during the fluid displacement phase is required to improve the fluid compatibility in mitigating this problem. The main goal of this thesis is to generate ultrasonic data for several commonly used materials in the oil and gas industry to prepare muds, spacers, and cements. A baseline study is conducted to measure the variation in sonic velocity of individual materials dispersed in water. The generated baseline database will serve as a reference point to predict the sonic velocity in the mixed fluid. A feasibility study is conducted to determine the practicality of ultrasonic sensors to determine the sonic velocity of different fluids. The result of this study poses new questions which have been answered in the static single additive experiments. A total of thirteen (13) commonly used drilling and cementing additives are analyzed using a custom-made ultrasonic setup. Therefore, fluids of different concentration of each additive are mixed and the average sonic velocity determined. The results of this study give an intrinsic insight into the effect of each additive on the sonic velocity. Finally, a proof-of-concept experiment is presented to display how the acquired knowledge can be applied in the field. Therefore, two (2) muds of different density are mixed and displaced on a benchtop setup. Fluid discrimination, density evaluation, degree of intermixing calculation and required volume for full displacement prediction is successfully conducted and presented. Most of the objectives of this thesis are successfully achieved and are presented in detail.

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Author: Maximilian Minihold

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To ensure energy supply for Munich in the future, Stadtwerke München Services GmbH (SWM) is planning to utilize extended reach drilling (ERD) wells for resource development. With ERD wells it is possible to increase the potential from one well site, by producing heat in locations with a high demand. Complicated and cost-intensive connections to the heating network can thus be avoided. Several wells have already been drilled in the South German Molasse Basin and drilling processes have been timely improved. Wells in this area have been realized at around 3.000 m horizontal departure (HD) for shallow depths and 2.500 m for deeper depths, but potential for more horizontal reach is available. In geothermal projects within the Molasse Basin in southern Germany, several wells are usually drilled from one well site. To ensure sufficient spacing between boreholes in the reservoir, boreholes are drilled horizontally away from each other. Firstly, with increasing horizontal distance of the target point to the drilling site, the technical effort, costs and risks increase. Secondly, increasing the horizontal distance allows a significantly larger reservoir area to be developed from one drilling site. The ultimate goal of this thesis is to design a new well concept that focuses on a horizontal departure of at least 3.500 m up to 6.000 m in shallow depths of less than 2.500 m true vertical depth (TVD), taking into consideration solutions to overcome the current limitations, such as Torque/Drag, Hydraulics and Drag during Casing/Liner running. The final well design concepts established in this thesis should act as a foundation for future geothermal ERD wells in South German Molasse Basin. The basis for this thesis is a conceptual project selected in the northern region of Munich. Based on the most demanding well path of this project, various well path variations are developed using constant parameters to ensure comparability. This approach also allows the simulation of various difficulty levels, inclusive potential limitations. A full well design is established for all wells, taking into account existing SWM guidelines, literature, and expert insights from various industry disciplines. The developed well design is explained using one exemplary well. From the simulations can be concluded that, due to the implemented technology and expertise, all wells can be technically feasible simulated regardless of the length of the well, with only small operational changes (e.g., no rotation necessary during drill string tripping in) needed. A singular exception occurs during drilling simulations in Section 4 for well Var 3, which necessitates a top drive with higher torque capability. The well design established in this thesis encompasses selection and optimization of challenging well paths, collaboration with industry experts for the development of drilling fluids formulations, a casing design aligned with SWM guidelines that incorporates insights from manufacturers for the selection of proven ERD casing connections, and the incorporation of floating equipment for a 9.5/8¿ liner as well as a drill string configuration based on companies¿ recommendations. Furthermore, comprehensive simulations, including torque, drag, hydraulics during drilling and running liner as well as cementation modeling are conducted.

Author: Kyriakos Aliatakis

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Failure of cement integrity is one of the main issues in the O&G during the life cycle of a well but also on P&A, that results in loss of production, safety, environmental and regulatory concerns. Primary cement might fail to deliver zonal isolation due to several reasons such as cement contamination, exposure to corrosive fluids, influxes, in-situ stress variations, etc. that can cause leaks, cracks and even micro annuli on the cement and casing. When such failures are observed and occur during the lifetime of the well, then remedial job must be performed in order to restore the barrier and well integrity by sealing those failures with the use of various sealant materials that can also heal the cement.
This master thesis focuses on resin for remediation by using epoxy resin mixed with conventional and ultrafine cement, due to resins several advantages over Portland cement such as higher compressive strength, lower shrinkage, better mechanical properties, adhesive bond strength and so on. Each slurry tests were conducted by following the API standards to evaluate the rheological behavior, shrinkage, mechanical properties of the new sealant as well as its injectivity was tested, by using the Inhouse Sealant Injectivity Setup that was also used in the previous project. After each completion of the API and injectivity tests for one of the compositions, the data was analyzed before moving on the next composition. The injectivity tests were conducted by pumping the sealants through three various tubing diameters, which are 1/4”, 1/8” and 1/16”, in order to show the new sealants pumpability and the effectiveness of ultrafine cement and solid-free materials.
The results of the experiments proved that, epoxy resin enhances the properties of the cement in terms of compressive strength, rheology, consistency, bond strength and so on as well as the injectivity of the new sealant, where both the conventional and ultrafine cement mixed with epoxy showed that the sealant flowed successfully from the 1/4” section without any issues. The tests for the 1/8” section started to show the effect of particle-granular size of the conventional cement, where some pressure peaks were observed in high flow rates but both fluids passed through. Lastly, on the injectivity tests for the 1/16”, for both sealants pipe blocking was observed when applying higher flow rates but the ultrafine showed best results in low flow rates unlike the conventional cement where few high-pressure peaks were observed reaching the pumps pressure limit.

Author: Martin Klaus Walter Graf

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One of the many restrictions of the contemporary drilling projects is how to extend the limits of available rig capacities without significant cost rising, this continuing problem will last because requirements to drill extended reach (ERD) wells and ultra ERD wells would be stay present. One approach addressed in this thesis is to use combined drill strings comprising conventional steel drill pipes (SDP) and aluminium ones (ADP). The objective of this thesis was to investigate the possibility to extend the operational range of common rigs by reducing the drill string weight and related torque and drag resulting values via change of the main pipe material to aluminium for the process. Another main purpose was to provide a technology evaluation and approach for the application of ADP with wired drill pipe (WDP) systems to drill new ERD wells through the aid of considering actual ERD wells from Sakhalin project. Consequently at the beginning the understanding of the main challenges and difficulties connected with ERD well construction and what benefits could be expected of combined ADP/SDP applications where illustrated. Afterwards an ADP/SDP assembly analysis background was formed under consideration of optimised pipe combination for current trajectory and factors, in addition an examination was conducted on variables for hole size vs. pipe size dependence to adjust a max. reach well. In the named 1st phase for the given ERD well the last three drilling sections of 16”, 12 ¼” and 8 ½” the combined ADP/SDP design was compared with an conventional SDP design, important calculated drilling values and economic considerations were outlined and presented in an compact shape. To examine the demanded limits of this ERD setting and to demonstrate its limits for a max. reach well, a 2nd and 3rd phase were tested in a similar way like in the first phase, however with an unlimited tangential section to examine the longest departure distance of that setting. The 2nd phase performs the examination for the 12 ¼” section of the relative design assemblies and the 3rd phase includes the last 8 ½” section of its associated design assemblies. The final part comprises the specifications of the chosen WDP system, more precisely the chosen tde powerline system and summarise the technology benefits. Subsequent estimation of reduced well construction time is evaluate, followed by a cost analysis and extend via a breakeven analysis one about tde powerline system utilisation for ERD wells. Finally, conclusion is made about technological and economic feasibility if ADP enhanced with tde powerline extends the current range of ERD wells.

Author: Yakhyo Karimov

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Downhole pressure management is critical to maintaining wellbore stability, particularly in deep-water and narrow-margin drilling environments. A key contributor to pressure fluctuations is the breakdown of gelled drilling fluid structures formed during static periods. When circulation resumes, additional pump energy is required to break the gel, and poor pump start-up practices can lead to sudden annular pressure spikes that threaten well integrity. Therefore, understanding and predicting downhole pressure changes while breaking down the gelled structure during pump restarts are of paramount importance. Despite numerous studies conducted in the past to investigate the relationship between pump start-up sequences and associated pressure changes, all of these studies utilized only surface drill data, neglecting downhole data for various reasons. This thesis investigates the relationship between pump start-up sequences and annular pressure loss by analyzing historical real-time surface and downhole data from multiple wells across different regions. Unlike previous studies that relied solely on surface data, this work incorporates annular pressure loss measurements to provide a more accurate understanding of downhole dynamics. To perform a comprehensive analysis and reach a sound conclusion, eight new performance benchmarks were developed in this thesis. In addition, the thesis aims to develop empirical and data-driven models that can be used to predict the magnitude of fluctuations in annular pressure loss during pump startup. The main findings of the thesis are as follows: The most critical parameters causing significant fluctuations in annular pressure loss are the incremental change in flow rate, connection time, and the annular space between the drill pipe and the wellbore. Among the five models examined in this thesis to predict the magnitude of fluctuations in annular pressure loss, Random Forest and polynomial regression demonstrated the highest predictive performance.

Author: Timur Berdiev

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Companies involved in the upstream sector are highly interested in improving their business processes. One of the ways to achieve it is to optimize the most investment intensive activity – the well construction. During the drilling phase, the largest cost factors are time-dependent and the earlier the well is put into production the faster the return of investments, therefore the main driver is the time. The optimization of cycle times must not jeopardize the safety of the process and quality of the well. Therefore, the purpose of the thesis is to develop a solution for a multivariate well construction optimization problem. The approach to the problem starts with describing well-known industrial methods for well construction improvement. At first drilling process is described from the project management aspect. Roles of proper planning, execution, and monitoring components in delivering the high quality well on time are elaborated. Next, the drilling data management is emphasized as a vital component for achieving efficiency gains during well construction. The constituent topics, including data acquisition, storage, quality control, retrieval, are described. For enhancing the planning phase drilling data analysis tools utilizing historical data have to be implemented. They include productive time and process control analysis, non-productive time (NPT) analysis, best composite time (BCT), learning curve analysis, benchmarking. To complement the traditional improvement methods the idea of combining the PDCA (Plan-Do-Check-Act) methodology with real-time time component is presented. That resulted in the developed framework for continuous improvement. The real-time components are state-of-the-art drilling software: Automated Drilling Performance Management (APDM), Simulation Module, and Mechanical Drilling Optimization Module. Their principles and functionality are described in the thesis as well as the data flow model for such a setup. A combination of traditional data analysis methods with the developed framework is aimed at the reduction of non-productive time (NPT) and invisible lost time (ILT), thus solving the problem of multivariate well construction process optimization. Additionally, the workflow for crew and equipment related operations improvement is developed as a part of the continuous improvement framework. The result is the standardization of these types of operations as a best practice. Finally, the application of the suggested improvement framework to optimize the BHA Run operation is described as well as the deployment of performance enhancement workflow for slip-to-slip connection operation is presented utilizing the video analysis software. The developed framework can be implemented by companies to optimize well construction process and achieve performance gains and higher profitability.

Author: Renat Dzhafarov

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In the conditions of market uncertainty, unstable oil price and development of oil and gas field with complex geological structure, the tasks of optimization and costs reduction for well construction become especially relevant for oil and gas producing and drilling service companies. The current situation is forcing companies to reduce volumes of drilling and abandon a number of planned projects. The time spent for a well construction basically depends on drilling crews’ qualification and coordinated work of all service organizations involved in the process. The means of increasing the work speed are not only transition to the use of more sophisticated equipment, but also rational and efficient organization of all processes. The thesis focuses on costs reduction for a well drilled by Gazprom EP International, which could be achieved with mud logging data processing using the ProNova data analysis system. Key features, advantages and disadvantages of the technology are discussed and potential time savings are calculated.

Author: Polina Gamayunova

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Gas production has been an important source of energy for humanity for over than 100 years. Due to the depletion of conventional and onshore Natural Gas fields engineers started to look for additional sources of hydrocarbons. One of regions which contain considerable amounts of Natural Gas resources is the North Sea. The shelf of the North Sea is a perspective region for Hydrocarbon development. However, it has a major amount of difficulties associated with drilling and production. Different technologies are used in the North Sea region to avoid or overcome problems which can occur during the process of drilling and production. Casing while Drilling (CwD) is one of technological solutions which are applied during drilling in this particular region. It has a number of benefits which ensure the expediency and profitability of application of this technology. Some of these profits are: reduction of Non-Productive Time (NPT), reduction of cost of drilling, occurrence of plastering effect, increased borehole stability and more. This work shows the case where Casing Drilling technology was applied for drilling surface casing section on a well, located on the North Sea shelf. Number of challenges were observed in similar intervals during drilling offset wells. These challenges include: potential clay balling, potential swelling formations, losses of drilling mud in the loose sands upper part of the North Sea group, “gumbo attacks” and over-pull on connections and trips. Considering all the data and history of drilling in this particular region a solution was purposed – application of Casing while Drilling technology. It is expected to help with all the expected difficulties, increase the efficiency of drilling and decrease the overall costs of the well and time required for its construction.

Author: Peter Mbah Tekum

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Reducing well construction cost per foot can be executed by several methods, focusing just on drilling performance and efficiency, which can be evaluated mainly by drilling speed, thus, a slight increase in average Rate of Penetration will definitely improve the overall drilling performance and efficiency and consequently, remarkably decrease in effective drilling time and reduction in overall cost can be achieved. Therefore, Rate of penetration (ROP) optimization has been a common research interest in the drilling discipline within the petroleum industry, being a very important topic especially during periods of low oil price, increased steel price and necessity to apply acknowledged expensive technologies. The ROP efficiency enhancement can be achieved through many different efforts, such as good well path design, optimum operational parameters, as well as implementation of novelty and innovative new technologies. In this context, ways of enhancing ROP while drilling has been an understandable practical and cost-effective method, and so has been in evidence for the last decades, covering research resulting in different approaches, models and methods, with reasonable application in the industry, but as evaluated, with rooms for improvements. Conceptually, many different ROP models can be found in the literature, which are mostly relates empirical models with specific coefficients that translate actual specific scenario to a mathematical equation, which defined, starts representing the relation between the drilling parameters and the ROP response that happened, allowing in seeking for set of parameters that may maximize ROP. Due to the many empirical coefficient and functional constraints involved for fitting, the representations have shown to have rooms for improvement, where novelty approaches have been valuable. In this perspective, this thesis details the research developed aiming an alternative method to predict and to maximize ROP based on drilling mechanics data, supported by machine learning techniques, which drove the attention since showed to be more robust, precise, and so a better way to mathematically model ROP response from drilling operations in combination to specific key operational parameters. This improvement when compared to previous models used was achieved by applying the Artificial Neural Network (ANN) and Random Forest techniques, followed by appliance of the Genetic Algorithm (GA) technique, all supported by the software and developed script in Matlab. Two models have been developed and were validated using real data. During the validation phase several cases were studied and noticeable conclusions have been reached, one of the most important is that the performance of the predictive models are function of several hyper parameters which have to be adjusted carefully to improve the efficiency of the models. The other important observation was that, the flow rate has significant impact on ROP optimization and must be considered when performing Drill Off Test.

Author: Rostislav Gupalov

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Companies engaged in the exploration and production of oil and gas in the North Sea very often face problems that arise when drilling salt formations. In this Thesis, drilling through Zechstein will be considered. In addition to the conventional problems that arise when drilling salt layers, there is the problem of floaters, uplifted or detached carbonate blocks on the flank of a tectonized fault zone. It was proposed to use managed pressure drilling (MPD) during drilling of these intervals. Accordingly, it is necessary to assess the feasibility of using this technology in such problematic areas. Project N is a development horizontal offshore well in the Netherlands in the North Sea operated by Wintershall Noordzee B. V. First of all, the basic information of a selected well will be presented. The geology of the section of interest will be described in detail, problems that may occur during drilling are identified. Also, seismic issues will be addressed, the probability of accurately determining the location of the floaters is estimated. Secondly, a general review of MPD technology, its categories, and variations, will be carried out. Attention is drawn to the use of MPD for drilling salt layers in the past. The basic MPD equipment is described, the availability of the platform, the use of which is planned in the project, for MPD is estimated. Besides, the stability of the wellbore largely depends on the mud program of the drilling process. Casing and cementing issues are also covered. The main problems that may interfere with the normal and reliable performance of these operations are identified. As a result, casing and cementing programs as well as their solutions are described in detail. For different problem interval drilling scenarios, the feasibility of using MPD is described, and for the case where the use of MPD is necessary, MPD Influx Management Matrix is developed. An important point is the economic component of this technical solution. Both the use of the MPD and the financial consequences of its non-use are estimated, as a result, the economic effect is obtained. After a detailed analysis, it was found that the use of MPD in this region is appropriate. Firstly, it was proved that without additional expensive geological studies it is impossible to determine exactly the presence of floaters. Secondly, when considering various scenarios, it was found that when encountering floater and subsequent kick of averaged intensity, the conventional drilling system is not able to stabilize the well, while the MPD allows safe drilling of the hazardous interval. Thirdly, the economic effect of the use of MPD plays an important role in the final solution. The use of MPD requires an initial investment, but the consequences of not using MPD in an influx situation far exceed these costs. Thus, the use of MPD in this section would help to save a lot of money and time and therefore is a suitable technical solution.

Author: Artyem Gorshenin

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With the development of the oil and gas industry, the health of the wells always stays in focus. Well, integrity is a critical matter throughout the entire well life cycle. The failure of the wellbore integrity can result in not only adverse financial outcomes and stability of an organization but also significant environmental consequences, including the pollution of groundwater, the release of gas into the atmosphere, and leakage and spillage of fluids on the surface. Tubular monitoring, in terms of well integrity, enables early detection of potential damage, especially in ageing wells. The structural integrity of wells may deteriorate over a certain period, increasing the likelihood of tubular failure. During the well production phase, tubulars are most susceptible to cyclic loads (axial loads, radial loads, bending loads), corrosion, temperature, pressure changes, etc. For instance, external casing corrosion is a common problem in the oil and gas industry, which can compromise the safety and productivity of the well. However, predicting the corrosion rate can be difficult due to the uncertainty of various factors. Since the accuracy of theoretical models to indicate the corrosion rate is questionable, inspection tools are frequently utilized to monitor the remaining wall thickness of the casing to prevent potential leaks and other hazardous incidents. However, different logging tools and sensors have some limitations when it comes to continuous measurements. Wireline logging jobs are periodic operations and can only be used when the well is in a shut-in state and when the tubing has been removed to enable logging in the casing string. On the other hand, fiber optic sensors are commonly utilized for acoustic, temperature, and strain measurements. These types of measurements are not capable of identifying localized corrosion types, and they come with high costs. A similar situation is identified in the tubular surface applications (pipeline). The pipeline inspection tools provide periodical health information and other monitoring technologies primarily based on existing leak detection. The thesis work aims to investigate mechanical changes in tubular, which are subjected to high pressures, temperatures, and exposure to corrosive fluids causing mechanical stress and deformation over time. To address the limitations of conventional logging tools and fiber optic sensors, the study proposes using new strain sensors for detecting tubular mechanical deformations. The proposed research aims to compare existing strain measurement technologies from a market point of view and define the most suitable applications for tubular integrity monitoring within the oil and gas industry.

Author: Faraz Feizi

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A significant component in the drilling operation is the circulation system. Drilling rigs have a crucial dependency on mud pumps, and a failure in the mud pumps will impose the drilling operation to stop completely; consequently, the drilling cost will increase due to the associated nonproductive time. Therefore, companies try to detect failures before occurring by implementing different techniques and strategies for improving pump operation time and efficient maintenance management to reduce or eliminate non-productive time, health, and environmental safety risks. Different tools and techniques that support the real-time monitoring of mud pumps have been proposed in the last decade; one of them is Artificial Intelligence (AI), which has shown promising results. Therefore, the ultimate goal of this thesis is to investigate the possibility of using artificial intelligence techniques to detect specific mud pump failures by utilizing only the pump pressure and flow rate as input features. This thesis is divided into three main parts. The first part of the thesis presents and discusses the general failure detection techniques and maintenance strategies. The second part of this work presents the common drilling mud pump failures and the impact of failures on drilling operation efficiency and HSE, and what are the state-of-the-art non-intrusive sensors that can be used to detect the pump failure signatures. The last part of the thesis elaborates on the steps of developing a conceptual approach based on artificial intelligence techniques to detect failures in drilling mud pumps. In order to validate and determine the limits of the developed tool, a case study was conducted using real historical data.

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Author: Tomislav Stanic

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Hole cleaning and cement quality improvement are considered some of the challenges facing energy extraction companies, especially for horizontal wells. One of the solutions proposed a decade ago to overcome these issues was Reverse Circulation (RC). Reverse Circulation has been implemented in many industries, and it has been proven to be a promising method with the potential to significantly increase drilling efficiency while reducing total drilling costs. In Reverse Circulation, drilling fluid is pumped from the surface into the annulus, where it then flows to the base of the wellbore. Cuttings from the formation are then transported back to the surface through the inside of the drill string. Despite numerous successful studies published on the utilization of RC for various purposes, there remains a common deficiency in the majority of these works. The limitations of applying this method and the necessary requirements are often inadequately explained. Therefore, the ultimate goal of this thesis is to look into the many uses of RC, including drilling, cementing, and hole-cleaning processes. In addition, it will highlight the unique challenges of RC drilling and point out the significance of comparing this technology against conventional approaches. The primary focus of this thesis is to explore the benefits and drawbacks of RC drilling, particularly in the context of fluid mechanics, limitations, applicable scenarios, and economic implications. Additionally, the thesis undertakes a comparative analysis of hole cleaning efficiency between Reverse Circulation and conventional circulation by constructing scenario cases using the eDrilling simulator. To conduct a fair comparison between the two methods, two Key Performance Indicators (KPIs) were employed: cuttings profile and cuttings transport rate. The performed case studies revealed that under lower or equivalent pressures, conventional circulation outperformed Reverse Circulation in terms of cuttings transport efficiency. However, with appropriate input adjustments, the best-case scenario for Reverse Circulation matched or even exceeded the performance of conventional circulation, demonstrating that the Reverse Circulation process can be optimized for more effective cuttings removal and wellbore stability.

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Author: Ilia Filippov

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Many E&P Operators are today assessing the viability of converting existing assets designed for production of hydrocarbons into assets designed for injection and permanent monitoring of CO2. This tendency is mainly driven by laws and regulations aiming at reducing CO2 emissions, and permanent storage in depleted reservoirs is seen as a great enabler to achieve just that. The number of CCS projects is growing because of the prospect to reduce the carbon footprint of oil and gas operations by converting existing production wells to CO2 storage wells. The use of existing wells has certain advantages. On the one hand, there is no need to drill new wells, thereby reducing potential costs, which will be particularly significant when drilling offshore. On the other hand, there is a safety aspect: the fewer wells that penetrate the caprock, the better the integrity of the storage is. The main objective of this work is to create a workflow of converting existing oil/gas production wells into injector/monitoring wells in CCS projects and adapt it to one or several company’s existing wells in the Dutch sector of the North Sea.

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Author: Felix Hahn

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Ensuring the long-term reliability and safety is the major challenge faced for geological CO2 sequestration projects. Since the wellbore of injection and monitoring wells are the most probable leakage path of CO2 into overlying formations, aquifers or even to the surface, well integrity is of utmost importance. Poor zonal isolation caused by failure of Portland-based cements used as annular sealant in these corrosive downhole environments needs therefore be thoroughly investigated. Since the carbonation of this material in presence of CO2 and water results in cement degradation. Therefore, innovative testing equipment in the form of the computed tomography (CT)-scannable in-situ test cell is used to determine the long-term effect of supercritical CO2 on the cement matrix under permanently maintained simulated downhole conditions. This master thesis presents the results of this long-term exposure test of a cement system to a corrosive downhole CO2-environment, with focus put on the evaluation procedure for the CT-scans conducted during the experiment. This procedure is based on application of artificial neural networks (ANN) and algorithms to assign the individual pixels of the CT-images to certain phases and afterwards conducting precise pixel-based measurements. The results show significant alteration of the tested cement if exposed to a corrosive downhole CO2-environment. Additionally, the initial function as gas migration pathways and the later auto-sealing capability of formed cracks within the cement core are pointed out. Especially the respective influence of these two occurrences, with a sharp increase in initial stages and gradual decrease at later stages, on the measured propagation rate of the carbonation front was characterized by the conducted measurements.

Author: Pavel Iastrebov

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Analyzing return cuttings during drilling is one of the opportunities, besides core analysis, to observe and characterize the drilled rock. It gives real time information needed for bit depth correction and lithology correlation, such as rock type, color, texture (grain size, shape and sorting), cement amount, fossils presence, porosity and permeability. Correct measurements of those parameters (shape and size distribution in particular) improves the drilling performance and anticipates possible problems and complications. Cuttings and cavings presence in annular space increase the Equivalent Circulating Density (ECD), which leads to higher pressure losses; they are also one of the causes of Rate of Penetration (ROP) reduction because of chip hold down effect. Their shape is the inference for probable causes of borehole instability and quality of the mud cake. Several techniques have been used in last decades for obtaining the return cuttings parameters, such as their relative amount, particle size distribution (PSD), size and shape. They comprise state of the art technology based on computer vision techniques with machine learning algorithms as a software. A number of such techniques is already available on the market, and have their limitations and advantages. Basing on this principle, OMV is planning to build in house intelligent and cost-effective system which is capable of determining the cuttings parameters in real time. The built system should be feasible from the point of proactive problem prevention, reduction of Non-productive Time (NPT) by well complications mitigation and simplification of tedious mud-logger labor. After carefully reviewing and studying the shortcomings of the recent techniques regarding cavings analysis, a conceptual design of automated cavings analysis technology is proposed in this thesis. The system is split into hardware and software parts. The first part includes circulation system for washing the cavings, as well as the camera and lightning facility. The camera is connected to the laptop with running software in the background, which is based on the Convolutional Neural Network (CNN). This algorithm analyzes the captured frames and delivers cavings’ shape, size and lithology as an output. Furthermore, feasibility study is conducted, in which rough costs of the proposed system are estimated.

Author: Alexander Bazoev

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Laboratory-scale drilling rigs open the opportunities for conducting investigations and testing of new equipment and technologies. Since field experiments with the real-scale installations are quite difficult, dangerous and expensive, the miniature rigs provide useful alternatives for innovative researches of drilling processes and creation of modern devices. The Montanuniversitat MiniRig is one of the few of its kind and its development is an important goal of the department. The installation includes all the main systems inherent in industrial drilling rigs: rotary system, hoisting and circulation systems. The key advantage of the MiniRig is the control system which is presented by programmable logical controller (PLC). With the use of PLC automatic drilling operations are implemented, thus the prospects of full automation of drilling rigs can be investigated. However, the current setup is not equipped with pipes hold and supply system. Therefore, it can¿t perform drill string connection operations in automatic regime to substitute manual work on pipes screwing. Such restrictions do not allow to fully implement experiments on automation and study of drilling processes. To enhance the functionality of MiniRig the continuous drill pipe connection system was designed. First of all, all the necessary tasks that the system should conduct were defined. The system combines pipe holding and feeding mechanisms and makes possible making up and breaking out operations in automatic mode. The next step involved determining of the general appearance and building the mechanical components using SolidWorks CAD. Also the limitations due to laboratory conditions are taking into consideration. The designed concept integrates a setback and a pipe supplier and represents the rotating cylinder with channels for pipes. Since at each moment of time one of the retained pipes is on the well center, drilling and tripping are carried out through the cylinder. Moreover, the pipe holding mechanism is used not only inside the channels of the cylinder, but also as slips near the drill floor. For the purpose of substantiation of the selected design feasibility the calculations of the key mechanical parameters of each unit were conducted. The outcome of the work is the model of the continuous drill pipe connection system which is accompanied by the main mechanical calculations. Next, the designed system will be built and automated.

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Author: Kseniia Zhukova

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The main goal of hydraulic fracturing is to create a highly conductive fracture system that will improve the inflow performance and increase the ultimate reservoir recovery. Not properly designed process leads to underperformance of treated wells and can negatively impact the reservoir. Accurate hydraulic fracturing design is of great importance for post-job efficiency. As in many other areas, the improvements are a natural consequence of previous measurement and detailed analysis. Therefore, evaluating the historical frac jobs could help to improve the planning and increase execution efficiency. During this master's thesis writing, a practical tool for evaluating hydraulic fracturing performance is developed. The tool is based on a data-driven approach that helps in interpreting real-time data. Proposed algorithms automatically classify each timestamp of the treatment schedule and assign the stage label. Support vector machines and neural networks are used to classify the operation stage. These models are trained and evaluated on the datasets recorded on several wells. This thesis aims to set the metrics that could be generated based on the hydraulic fracturing job monitoring and provide valuable feedback about job efficiency. Defined metrics and a data-driven approach help understand and measure historical data that could be a valuable input for further designs and identification of potential savings of materials utilized in operation.

Author: Arseniy Shcherbakov

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From year to year, the well construction process becomes more challenging, the oil and gas industry requires new technologies or upgrades of existing ones to ensure high efficiency and reliability of the drilling process. Enhancement in the construction feasibility indicators of deep, branched, complex profile and extended reach drilling wells can be achieved through the promotion of technology developed in the middle of the last century and applied in the oil and gas fields of the USSR ¿ electric bottomhole drilling. This technology combines the benefits of drill string with conductor lines and ideal downhole motor, that is independent of the drilling mud type and has a wide range of revolution rates. The new generation of submersible permanent magnet electric motor (PMM) and the new drill string design with power conductor lines (DPC) will have improved performance capabilities that can potentially eliminate the shortcomings of the previous generation. The features of DPC operational process for ensuring PMM exploitation will be considered in the master thesis. DPC pressure losses analysis in comparison with conventional drill pipes for rotary drilling with hydraulic downhole motors are demonstrated. Analytical and numerical analysis of power conductors affection on pressure losses in DPC were conducted. To further clarify the conductors affection, plan and methodology of experimental test on Neftekamsk Machinery Plant of Special Equipment are presented. The dynamic analysis of DPC operational process for observing sensible design parts with DYNTUB software and bench test preparation are proposed.

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Author: Artem Karimov

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It is quite common for logging while drilling (LWD) tools to be unstable and the acquired data to be of poor quality. This is why quality control of LWD data is of utmost importance. Common methods of quality control for wireline logs in vertical wells often do not show good results in horizontal wells because of vertical and horizontal heterogeneity of reservoir rocks. A quality control system and the ways to control the quality of common LWD methods are discussed in the thesis. Two approaches to control the quality of LWD methods are considered in the thesis. One of them is cross-plot analysis and comparison of obtained logs with offset wells and core data. The other is solution of direct and inverse problem from obtained well logs. The methods are compared to a typical way of histogram analysis and normalization. Examples of poor and good quality logs are analyzed in detail. In addition, problems, which could be encountered if proper quality control is not used, are discussed. The result of the thesis is a quality control system for processed LWD data in horizontal wells. The approach was tested in various lithological conditions: siliciclastic, salinated and carbonate reservoirs. The proposed system could be used to avoid poor decision-making during the process of geosteering and well completion.

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Author: Stefan Erakovic

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Casing leaks are a common issue in the oil and gas industry that might lead to severe production problems. Corrosive fluids often cause casing leaks, as well as prolonged exposure to corrosive gases, casing fractures under pressure, or casing wear from extended periods of drilling work. While drilling, the cementing process is done between the formation and the casing or between two casings to provide zonal isolation and well protection. If the cementing process is done poorly, a well barrier can fail, and cracks and micro-fractures can appear, allowing corrosive fluids to migrate. This can slowly corrode tubing and casing over time. Another possibility for casing corrosion to occur is from fluids flowing inside the wellbore, leading to the same consequences. Thus, casing leaks must be detected early to prevent these losses, which can result in substantial expenses. This master¿s thesis is focused on casing leak remediation by using conventional and ultrafine cement, as well as epoxy resin. Each fluid was tested according to API standards, and later, the injectivity tests were done for that fluid in the casing leak setup, which was developed in the previous master¿s thesis. Upon completing the API and the injectivity tests for one fluid, the data was analyzed, and the next fluid was tested. As a reference point, injectivity tests for water were also conducted. The injectivity tests of cement and epoxy resin were done using three different internal tubing diameters, which include 4,572 mm, 1,753 mm, and 0,774 mm. The results of the experiments demonstrated that all fluids successfully passed through 4,572 mm internal tubing diameter without problems. The injectivity tests for the 1,753 mm internal tubing diameter showed the influence of solids inside the liquid, with the conventional cement slurry starting to plug and the pressure spikes starting to appear. Other fluids passed through successfully without issues. The injectivity tests for 0,774 mm indicated that only solid-free liquids like epoxy resin can guarantee a successful casing leak remediation. However, due to the high cost of epoxy resin, an attempt should be first made with the ultrafine cement slurry.

Author: Aleksandr Geraskin

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Gazprom EP International and Yacimientos Petrolíferos Fiscales Bolivianos (Bolivia’s state-owned oil and gas company) reached an agreement in June 2018 to explore and develop Vitiacua license area, located in the southern part of Bolivia, by joint efforts. Promising block will become the part of existing system in case of gas condensate field discovery. To prove the presence of hydrocarbons and declare commercial viability of the project, Gazprom and YPFB have a plan in the near future to drill the first exploratory well in that area. In respect to this fact, development of technical documentation for the well construction are relevant tasks for both companies at present time. Considering the fact that drilling conditions in Sub-Andean foothills are characterized by a number of distinctive challenges (geological, technological, technical and issues related to logistics), the process of well construction might take several years to reach target depth. Accordingly, well planning is the key issue for the first exploratory well within perspective block. Elaborated planning of well construction process will allow to reach better key performance indicators and reduce non-productive time during project execution. Challenging drilling conditions require implementation of integrated approach to well construction to make substantial change in advancing drilling performance. In the context of planning phase of the Vitiacua-1 well, the prime goal of the thesis is to develop comprehensive drilling program which covers aspects of planning from wellsite selection to well construction time estimation. The first part of the thesis covers identification of non-productive time root causes in Sub-Andean region and associated geology related drilling hazards, offset wells construction time analysis, determining the potential area for improvement in the prospective VItiacua-1 well. The second part is specified for exploratory well technical design comprising key elements of drilling program: geological information, casing and cementing design, drilling fluid, directional drilling program, well control and formation evaluation summary. Third part provides time projection and cost estimation for Vitiacua-1 well. The last part is devoted to the strategy proposed for improving drilling efficiency in the planning well. It includes different cutting-edge technologies and tools overview, advice for high-quality drilling performance indicators monitoring in real-time and general recommendations for improving drilling process.

Author: Emanuel Hofer

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This thesis covers the methodology of the development of a data analysis tool for designing kick-off plugs as well as laboratory-based simulations and experiments in order to validate the prediction quality. The data analysis tool can be used to design cement plugs and to simulate the consequence of specific fluid rheological parameters as well as distinctive selected parameters on the outcome of the plug job. The goal of this thesis is the implementation of a simple, field applicable and intuitive program that enables the engineer to design a kick-off plug that fulfils all requirements for a successful placement of the plug on the first attempt. The thesis describes the development of the data analysis tool starting with a detailed literature review where the most prominent industry related cement plug issues are described in more detail. Based on the assessment, a root cause analysis is implemented that reduces the common plug problems to four distinctive elements. Following the root cause analysis, the development of the design software and its individual modules are explained in detail. All four elements as well as the basic workflow and their structure are illustrated properly. In order to validate the outcome and the prediction quality of the software, laboratory-based simulations are executed. Prior to executing lab simulation runs, they were mathematically simulated using the data analysis tool. Afterwards predicted parameters and observed laboratory results are compared and rated. In addition, computed tomography images (CT scans) support the assessment and enable a direct look into the laboratory produced kick-off plugs. In a last step, a novel compressive strength enhancing material is tested. Therefore, the compressive strength behaviour of a neat Class G cement and fibre reinforced cement cubes are compared and benchmarked. Recommendations as well as results and future work steps can be found in the appropriate sections as part of the discussion and conclusion chapters at the end of this master thesis.

Author: Andreas Ortner

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Stuck pipe events are operational challenges which contribute to non-productive time (NPT) and increase the associated drilling costs. It is estimated, that the costs of stuck pipe events sum up to hundreds of million US dollars annually. Approximately 25 % of the non-productive time during the drilling operation is caused by stuck pipe events. 30,5% of all those stuck pipe events are associated to be differential sticking. A drill string or bottom hole assembly can get stuck due to differential pressures if part of the string is subjected to a different pressure (formation pressure) than the hydrostatic pressure in the wellbore. However, it is claimed that differential stuck pipe can be prevented when certain best practices are applied strictly. Incorrect operational parameters, incorrect procedures, unknown formation properties, and BHA design can lead to differential stuck pipe events. Once a pipe got stuck it might take enormous effort to free the string again which increases non-productive time, increases the drilling costs and might cause safety issues. There exist several best practices for avoiding differential stuck pipe and for relieving the pipe once it occurred. Detecting an upcoming stuck pipe event relies on the experience of the operating personnel and their interpretation of the drilling parameters. The aim of the thesis is to use a state-of-the-art drilling simulator to create realistic training cases based on best practices. Students and professionals can train on this simulator to improve their skills. Further, the reduction of NPT due to training should reduce drilling costs and increase safety.

Author: Sahand Shams Eshaghi

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The fluid displacement is being assessed and evaluated via digital sensing of involved parameters such as flow rate and pressure in lab-scale apparatus known as a flow loop. Flow loop replicates the geometry of the borehole and the casing/drill pipe in a lab scale (5 meters) manner. The thesis has 1 major objective and 1 minor objective. The major objective is to compare experimental results with a commercial software. The series of tests included 6 different non-Newtonian fluids at 4 selected flow rates and 3 selected standoffs leading to 72 experimental tests. During the test, parameters such as flow rate and pressure were recorded by sensors in real time and the processed results were compared with software simulation. Since a picture is more than a thousand words, the interface between fluids is tracked and digitalized by digital cameras (2 high-speed and 1 GO PRO). The visual tracking of the interface provides a better understanding of interaction between two fluids during displacement process in real time. The displacing fluids are designed and provided by a client and the displaced fluid at this phase of the experiment is water. Because horizontal well has more complexity than vertical and inclined, the horizontal was selected for the first phase, but in the next phases, other inclinations will be included for tests. Amongst the 6 fluids selected for displacement, 3 of them have translucent optical properties and 3 others are opaque (Barite as weight up). The water as displaced fluid was placed in the annulus and displacing fluid was pumped from the bottom of the flow loop to the annulus. The fluids had a density ranging from 8.6 to 12.8 ppg, from low to high viscosity and yield point. As a minor objective, the digitalized interface tracking was compared with available literature to investigate the validity of the observed interface. The content of the thesis is summarized in 6 chapters. The first chapter gives an overview of the issue and the objective. The second chapter describes the available literature review and previous studies. In the third chapter, the flow loop technical setup and configuration and capability are put forward. The methodology and calibration of sensors and digital tools were described in the fourth chapter. Results are discussed in the fifth chapter and the conclusion and alternative solutions are explained in the sixth chapter.

Author: Aleksandr Verkhozin

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Currently used mud pulse telemetry technology has some drawbacks which limit the economic viability and feasibility of extended reach wells construction. Wired drill pipe technology as a means to transmit downhole data is being considered. The thesis focuses on economic feasibility assessment of wired drill pipes application for extended reach drilling through time and cost analysis. The main project partner is OMV. The project has three advisors: Antony Martin (OMV), Prof. Gerhard Thonhauser (Montanuniversität Leoben), Prof. Aleksandr Oganov (Gubkin University). History of wired drill pipe technologies is provided in chapter 2. The next chapter describes WDP enabled benefits in macro-areas of drilling, formation evaluation, production, and power supply. After that, two commercial wired drill pipe systems – IntelliServ and Powerline Drillstring – are highlighted. Two extended reach wells are considered in the case study. Time savings resulted from implementation of wired drill pipe telemetry are calculated first. Then cost analysis of wired drill pipes utilization is conducted taking into account wired drill pipe related operational and capital expenditures and cost savings resulted from time savings. Finally, the author concludes whether wired drill pipe technology can make extended reach drilling more economically viable.

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Author: Artur Khusnutdinov

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Horizontal drilling for production wells has almost completely displaced the vertical and conventional directional drilling, which led to the significant revision of drill string technical requirements. The need for constant monitoring of the technical condition of various drill stem elements is becoming a mandatory process. Moreover, one of the most widespread accident in drilling is a drill stem failure including pipe washouts and drill string breakdowns. The issue of early prevention of drill stem accidents has always been a critical question since the rotary drilling appearance. For example, an accident analysis on the areas of the Timan-Pechora province indicated that 42% of all accidents from 1971 to 2013 are accidents with drill stem elements. This is a statistics without taking into account sticking (Kamenskikh 2015). However, even since 2013, the speed and footage of drilling has increased significantly. Drill string failures due to fatigue wear of the pipe body and tool joints has become a common problem in drilling companies. In addition to the non-productive time spent on the elimination of such accidents, companies suffer huge losses associated with the disposal of nonserviceable pipes and expensive bottom hole assemblies (BHA) left in the well. The thesis focuses on a problem of drill stem failures during drilling of high-tech wells in the East Messoyakha oil field. Key features, conditions and causes of accidents are discussed. The ways to eliminate the same problems in the further work are considered and estimated from economic and technical point of view.

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Author: Stefan Lebwohl

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Carbonation of Portland-based cement systems poses a significant risk to well integrity in the harsh environment of CO2 injection wells. Due to the corrosion potential of CO2 in conjunction with water, the cement matrix is attacked, resulting in cement degradation. Therefore, a fundamental knowledge of the ongoing changes in physical, mineralogical, and mechanical properties within the cement matrix and the propagation rate of the carbonation front has the highest priority to ensure well safety throughout its entire life cycle. In this thesis, an innovative, in-situ, computed tomography (CT) -scannable test cell will be presented, enabling unprecedented research on the carbonation propagation over time. Furthermore, with this pressure cell, a system permeability indication, real-time monitoring, and cement curing within the cell under simulated downhole conditions were realized. The carbonation resistance of the specially designed cement was additionally investigated by an autoclave experiment, where the cement samples were exposed to a supercritical CO2 environment for 28 days. Mineralogical investigations, such as optical microscopy, scanning electron microscopy (SEM), element mapping, and X-ray diffraction (XRD) analysis provided insights into the cement matrix alteration and the distribution of cement phases. Compressive strength tests were conducted on the untreated and CO2-exposed samples to evaluate the cement¿s strength alteration. The results of the mineralogical investigation show that the cement matrix was significantly chemically restructured by the influence of CO2. Both the autoclave and in-situ test cell experiment verified a self-healing effect due to calcium carbonate precipitation. Impressive results were obtained by the CT-scan analysis. These show that the propagation rate of the carbonation front reached a maximum after CO2 injection and declined steadily with time since a protective layer was formed.

Author: Paya Roknian

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Well integrity is one of the most important concepts in the upstream oil and gas industry. No matter whether a well is in drilling phase or has been already completed, the well integrity should be maintained. It is a multidisciplinary approach and has always been a serious challenge for major oil companies, regardless of operator or contractor. Therefore, all various departments in an oil company including drilling, completion, production, and plug and abandonment must cooperate and apply different methods, software and hardware, in order to maintain the well integrity for each operation of each section of each well. This research work aims to perform ultrasonic measurement as a non-destructive evaluation method (NDE) to estimate the compressive strength of oil well cement with different densities and recipes at several ages. Therefore, the main project’s target is to find a correlation between these two mechanical properties of oil well cement, the uniaxial compressive strength and the ultrasonic wave velocity, by inducing ultrasonic waves into the specific cement with unique composition at the known age. Using the correlation allows estimating the compressive strength of the cement in various densities and formulations other than the ones used in this project. As to the methodology, six cement compositions with different recipes have been chosen for the linear measurement tests in which the ultrasonic wave velocity is correlated to the compressive strength of oil well cement. Additives used to prepare a wide density range from 11.0 to 16.0 ppg include barite, bentonite, and 3M glass bubble. Different regression methods have been tested only best, with the highest R2 of 0.96 chosen to estimate the strength for 2D models. The factors considered in the model as input include water-to-cement ratio, density, ultrasonic wave velocity, and age. The result shows that the composition with higher density, made by barite, is more resistant against being fractured and can convey an ultrasonic wave faster, while the lightweight cement, bentonite, and glass bubble made, has a lower compressive strength and a slower ultrasonic wave velocity. Moreover, a function model is created based on the correlations between compressive strength, ultrasonic wave velocity, age periods, and density. The model's inputs are ultrasonic wave velocity, age, and cement density, while the compressive strength is the model’s output. Moreover, by using the acquired data, different correlations among (UCS, density, age) and (UCS, UWV) and (UCS, age) and (UWV, age) have been shown all of which have accuracy above 0.96 R2. Among the 2D correlations, UWV showed the best power fit for all cement samples. Eventually, by employing the 2D correlations and their generated coefficients, a rigorous analytical approach was given to define a generic 3D model of UCS as a transcendental function of several variables, including the density, age, and UWV. The function obtains the accuracy of R2=0.77. The modeling was a rigorous analytical approach. In case more data is generated in future work, the accuracy of the model can be improved. Another approach to improve the inherent accuracy could be employing machine learning techniques to get the best fit in transcendental functions rather than algebraic functions.

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Author: Sharen Leon

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Wellbore instability problems are frequently encountered in drilling operations. Large cavings, which are recovered on the shale shakers, are the most prominent indicators and often give an abundance of information. For instance, the evaluation of the micro-fractures and the interaction between the drilling fluid and the shale itself, which are key factors to draw a better conclusion of the possible cause and prescribe solutions to prevent such problems in the future. By analyzing the samples of cavings obtained from a caprock shale of an oil field in Mexico, this master thesis aims to propose a methodology to better understand the root cause of the wellbore instability problems in this type of formations. The wellbore instability problem presented in the Mexican onshore wells included in this master thesis is associated with micro-fractured shale, anisotropic failure and weak bedding planes. This is evident by the appearance of three to four centimetres tabular cavings which causes a main problem when controlling the well and handling the cavings on the surface. This study covers in an integrated manner, real-time monitoring data analysis, geomechanical analysis, micro-CT scanning, shale characterization as well as an experimental set up of the HPHT (High Pressure High Temperature) filter press use for permeability plugging tests. The proposed setup of the HPHT filter press is designed to analyze the pore plugging effects in shale as well as the interaction between the drilling fluid and the actual rock. This is achieved by developing a replacement of the conventional ceramic disk with the shale samples obtained from the cavings. A methodology to prepare disk for the permeability plugging test from shale cavings was developed and is presented. The results of the laboratory tests, the geomechanical analysis and the shale characterization give us a better understanding of the behaviour of the shale under borehole conditions, the in-situ stress state of the area and the possible causes of the problem. The methodology applied in this thesis can be beneficial to optimize the selection of the LCM (lost circulation material) by analyzing the micro-fracture width in relation with the pore plugging effects.

Author: Mislav Halilovic

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Preventing formation damage is the primary objective of a drill-in fluid. Damage can occur through many different mechanisms including emulsion blocks, water blocks, polymer/filter/particle invasion, precipitates, and improper wetting of formation. Damage can be remediated by stimulating the formation through fracturing, acidizing, or improving flow-back with chemical treatments; however, these post-drilling treatments can significantly increase well construction costs. One of the critical factors in designing non-damaging fluids to prevent fluid invasion is by sizing particles in the system to obtain a surface bridge on the formation face with minimum in-depth solids penetration. The other one is conventional drilling fluid additives need to be replaced with non-damaging ones. Evaluating formation damage and filter cake degradation is usually done by Permeability Plugging Apparatus (PPT) and static high-pressure high-temperature filter press (HPHT). These two devices mimic only the flow in one direction which occurs while drilling. The mast of drill-in fluid vendors claims that the internal and external filter cake, that has been developed while drilling, could be removed once the production started due to differential pressure applied in the reservoir during production. However, prove this concept in the lab using the HPHT filter press can be done by adding specific engineering design features to the existing HPHT filter press. In this regard, the ultimate goal of this thesis is to develop a pioneering apparatus that can be used to evaluate the degradation of the filter cake by measuring two intrinsic indexes. The developed apparatus is designed in a way that it can be integrated with devices used to evaluate the static filter cake. It has two modes of operation, closed mode and flowing mode. The closed mode is used to measure the filter cake lift-off pressure, whereas the flowing mode is used to evaluate the filter cake removability index. The resultant indexes can be used as Key performance indicators to compare the potential formation damage caused by different Drill-In Fluids or to compare the efficiency of different breakers used to remove filter cakes. In order to test the functionality of the developed apparatus and establish standard test procedures, several experiments based on short term static filtration tests have been performed. The experiments were conducted using a drill-in fluid with various formulas and under carefully selected conditions. The results demonstrate that the newly developed tool capable of measuring the intended indexes smoothly within a short time and without troubles.

Author: Karin Gurtner

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Casing leaks are a major problem in the entire oil, gas and geothermal energy industry all over the world. The reasons for casing leaks are multiple, but the majority of the failures is due to corrosion and mechanical wear, because of reciprocating or vibrating artificial lift systems. Additionally, wellbore treatments such as acidizing or fracturing are well known to be another major source for casing failures.
The impact of casing failures is usually phenomenal and in the worst case scenario the wellbore has to be plugged and abandoned. In this Master Thesis several options are discussed in order to repair the casing failures. The most common methods in the industry in order to overcome this problem are mechanical or chemical solutions. QHSE aspects are considered for every application. Mechanical solutions are most reliable, however the inside diameter of the borehole is reduced and therefore another barrier for the installation of artificial lift systems is created. In such a case the operator must be aware that after such an installation the original productivity of the wellbore cannot be achieved anymore. Repair methods like casing patches, expandable tubulars, and swaging operations are discussed in detail. Chemical solutions like the injection of specially designed cement slurries or resins or a combination of both of them have been investigated. Several methods like low pressure squeeze, high pressure squeeze and running squeeze have been discussed. The design of the cement slurry and all the relevant rheological and chemical parameters has been investigated.
The Master Thesis comprises a comprehensive literature review and analysis of 244 real case scenarios from the Vienna basin. The data sets were supplied by a business partner who operates the wellbores in the Vienna basin for more than 80 years. Therefore, it is obvious after such a long period of production the data material submitted is ideal for investigating in the subject of the Master Thesis.
Furthermore, numerous lab tests on various cement slurry designs have been carried out in accordance to the API standard “API recommended practice 10B-2”, and an optimized slurry design has been sorted out. The optimization criteria have considered Conventional-Cements, Microfine-Cements and Ultrafine-Cements. The type of cement to be chosen predominantly depends on the boundary conditions given by a particular wellbore problem and design. During the execution of the lab test it has turned out that especially the particle size of the cement grains, the density and the rheology of the cement slurry are the main criterion for choosing the right cement for the individual application. Additionally, quality checks on cement slurry samples have been carried out and crosschecked with the data sheets delivered by the cement manufacturer. It has turned out that the data sheets from the manufacturer are most reliable and of crucial relevance for the operators.
The specific test setup for the laboratory test are discussed in detail and documented and calibrated. The existing infrastructure is therefore ideally tailored for future lab tests and master theses.

Author: Mark Felix Putra Jaya

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With the trend towards increased drilling of high-temperature wells, as well as the requirement to use eco-friendly drilling fluids, additional demands are being placed on water-based drilling fluids (WBDFs) to address issues such as high-temperature flocculation of clay particles and to reduce fluid losses. Higher temperatures in deep well drilling are known to have effect drilling mud rheological and gel properties; the gel strength being the most affected as compared to viscosity. In order to counter high-temperature effects, which can flocculate bentonite or clay additives it is required to minimize the solids content and maintain the use of stable flocculation control. Another significant issue when drilling high-temperature wells using WBDFs is formation damage and wellbore instability caused by fluid invasion.
This study will focus on examining 3 types of WBDFs with two potential environmentally safe additives for each purpose, Sodium Tripolyphosphate Technical Grade, 85% (STPP) for flocculation control and Suspension of Cellulose Nanocrystals as a filtration control. The sequences are started with preparing the equipment and drilling fluid samples, ageing the drilling fluids at desire high temperature application either 140oC or 160oC depends on the WBDFs type for 16 hours, then respectively tested for flocculation and filtration measurement, followed by mud density, pH, rheological measurement, then finalized with performing thixotropy and hysteresis measurement.
From the three types of Water Base Drilling Fluids (WBDFs), which have been evaluated on this Master Thesis, for flocculation control, STPP with 0.1% is proven to improve Clay Water Base Drilling Fluid (CWBDF) with 65% liquid yield recovery which is better than CWBDF main composition, and with the other two STPP concentrations added to the main composition. While for filtration control, 0.5% Cellulose Nanocrystals (CNC) concentrations can decrease filtration volume of CWBDF to 17 ml while providing sufficient filter cake of 3/32” which is providing the better result than the other BWBDF compositions tested. Overall, STPP and CNC works best for CWBDF than Clay Polymer Water Base Drilling Fluid (CPWBDF), and Polymer Water Base Drilling Fluid (PWBDF). From the experimental results and analysis, both STPP and CNC have been showing a good result to improve drilling fluids performance when applied for WBDFs in high temperature application.

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Author: Stefan Weiskirchner

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Efficient displacement of fluids in annular geometries is essential in the oil and gas industry, particularly during primary cementing operations where achieving zonal isolation is critical for well integrity. Achieving good displacement can be a challenge in horizontal or highly deviated sections, where the eccentricity of inner pipe tends to be high. Eccentricity leads to non-symmetric velocity profiles and to wide and narrow annular gaps, which significantly impact the displacement process and can result in poor removal of remaining drilling fluids during the cementing process. Such conditions often lead to inaccurate pressure drop predictions, which can result in exceeding the equivalent circulation density (ECD) window and can lead to formation damage, well control issues or well integrity problems due to weak cement sheath caused by poor fluid removal. This thesis investigates pressure drop characteristics and displacement processes of non-Newtonian fluids in concentric and eccentric annuli through a combined experimental and numerical approach. A laboratory Flow-Loop is used to gather experimental data on four different fluids, exhibiting power law and Herschel-Bulkley behavior. The results were benchmarked against a computational fluid dynamics (CFD) replica of the Flow-Loop, developed in the well-known Ansys Fluent platform. Additionally, an easy-to-use laminar pressure drop calculator was developed for fluids represented by the Herschel-Bulkley model. The findings demonstrate a good comparability for single fluid laminar pressure drop between the experimental results and numerically simulated data. While the displacement process findings show a strong agreement for the displacement efficiency, the results highlight the sensitivity of front shape to variations in eccentricity.

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Author: Alexander Rekin

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Mechanical Specific Energy (MSE) is a key concept in drilling engineering that is used to quantify the energy required to drill a unit volume of rock or formation. It serves as a crucial parameter for evaluating drilling efficiency and optimizing the rate of penetration (ROP). The primary drilling parameters influencing MSE include downhole weight on bit (WOB), downhole revolutions per minute (RPM), torque on bit, and flow rate. While MSE in vertical wells can be estimated using surface-measured values of these parameters (except torque), this approach does not apply to horizontal and deviated wells due to discrepancies in surface readings. These inconsistencies present significant challenges in real-time MSE estimation. Although downhole drilling parameters related to MSE can be directly measured using Measurement While Drilling (MWD) tools, real-time applications are hindered by sampling delays and data processing constraints. To address this, several models have been developed over the past decade to estimate downhole parameters based on surface drilling data. However, these models often rely on predefined coefficients, which can limit their accuracy and adaptability across different well conditions. This thesis aims to evaluate the accuracy of existing models which are used for estimating downhole drilling parameters and propose modifications by integrating additional factors to enhance prediction accuracy. Furthermore, the study explores the application of machine learning techniques in predicting downhole drilling parameters, with the goal of improving MSE evaluation. The findings of this research indicate that existing models struggle to estimate downhole parameters accurately, particularly in deviated wells. However, the modified models proposed in this study demonstrate improved accuracy. Additionally, machine learning techniques provide promising estimations, though they have certain limitations that must be addressed for practical implementation.

Author: Nico Masching

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In the course of this master thesis, high-speed camera images were analysed to draw direct conclusions on the efficiency of fluid displacement processes as they occur in primary cementing operations in the oil and gas industry. These are about ensuring the integrity of wells, using cement as a well barrier element, which is inherently difficult due to complex trajectories and great depths. In addition to efficiency, it was also an objective to determine the degree of intermixing by means of optical spectrometry. An individual experimental setup, consisting of several components, first of all a transparent Plexiglas tube simulating a well, was created to visualize the displacement process. The generated images were analysed by means of a specially created Python program code using thresholding methods. All spectrometer data was processed and analysed. In all experiments, non-Newtonian drilling fluids with additives commonly used in the industry were utilized. The code used to analyse the displacement process has proven itself and the spectrometer has turned out to be a promising novel technique for investigating the degree of intermixing and its impact on cement integrity.

Author: Dmitrii Zenkov

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Sand production is complex problem that requires solution before the production at field planning stage. It is important to solve it by careful sand problems and affecting factors analysis with subsequent comparison of sand control methods to choose the best option for implementation. In this thesis, we describe the guideline for Frac Pack design based on completion experience on Astokh Field. We use logging and core data analysis in order to prove the necessity of sand control methods with accurate attention to XXI-layer as previously detected sand production target. Then we describe compound procedure consisting of perforation, proppant, screen and fracturing fluid recommendations. The main part of this thesis involves Astokh field completions description, its results and possible underperformance reasons. By the example of the most representative case, we made surface and downhole equipment review including frac pack treatment procedure with respective pre- and post-jobs necessary for its implementation. Based on this review the subsequent workflow was created. Finally, economical evaluation was done to find out if frac pack completion was successful or not. The proposed methodology in this thesis can be used in future completions on Astokh field or other fields with analogous characteristics.

Author: Andreas Lindner

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Unplanned and unexpected events during drilling a well do not only lead to a massive loss of resources by increasing the amount of non-productive time, but also cause the necessity of plugging a well and starting a contingency side-track, which will add environmentally and economically risks to the originally planned project. Therefore, detecting the undesirable downhole drilling trouble at the earlier stages may help avoid the matters above. Several surface drilling parameters can be used to predict the downhole drilling problems in real-time. Nevertheless, torque and standpipe pressure are considered to be the most critical and useful parameters. Therefore, several methods utilizing the two indicated surface parameters for detecting the downhole drilling problems were published in the last decade. However, these methods have flaws, mainly related to delays in receiving the necessary information, uncertainties associated with involved data, human error by potential incomplete data sets (due to sensor misreading), as well as human error interpretation of the data. Thus, linking sequential pattern recognition for possible drilling event determination is impacted. Consequently, recognizing drilling parameter anomalies in real-time using one single approach, such as data-driven or model-driven, can lead to an excessive increase in the nonproductive time due to the generation of undue false alarms. Thus, integrating a stochastic model with a datadriven model will reduce the associated uncertainties and make the predictive model more effective. From this perspective, the ultimate goal of this thesis is to develop a hybrid model that provides better accuracy in detecting abnormal behavior of measured drilling parameters such as standpipe pressure and torque. A standalone application based on a hybrid model was developed during the thesis work by the implementation of statistical calculations based on actual and predicted data channels. As a result, uncertainty windows are created and compared to the actual data points in order to detect abnormal drilling behavior and triggering alerts to provide warnings to the user. In order to evaluate and determine the shortcomings of the developed workflow, the developed hybrid model, a case study was conducted. The final results of the case study reveal that the workflow is reliable and easy to use.

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Author: Daniel Angyal

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The speed of a drilling process is predominantly influenced by the properties of the penetrated formation. Drilling plans are mostly based on previous experience in the field (if exists) and the expected geological circumstances. Although geological information is rarely 100% accurate, non-expected geological formations could still cause trouble, thus a tool which could provide information about current geological circumstances could be in great use. Studies show that there is a connection between drilling parameters and formation properties. In this thesis work, an investigation will take place on the correlation between drilling- and geological data of existing wells, located in Austria. Statistical methods will be implemented on depth- (and time-)based drilling data to create well defined groups which can be connected to a certain type of formation. The preparation of input data set for the machine learning algorithm is a crucial task of such a work. Different types of filtering, harmonization of additional data sets, and various plotting techniques will be presented in the thesis. The scope of this work is to find the connection between drilling and formation parameters and then develop an algorithm which can determine the geological formation based on drilling data, using machine learning.

Author: Adel Ahmed Ibrahim Eid

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Ordinary Portland cement (OPC) is the primary material, which is used in oil well cement, isolation formation and plug and abandonment. OPC has many advantages and some limitations reviewed by different authors. The limitations associated with cement cause well integrity issues, risking humans, and environment. Several studies and experiments are conducted to evaluate different materials, which could be an optimal alternate to OPC. Geopolymer is one of these materials, which has been tested in lab scale to find its potential to replace OPC. Geopolymers are inorganic materials based on rock sources, which are rich in aluminum silicates. Many pieces of research have conducted on the geopolymer to assess its characteristics and properties. Studies showed that geopolymer is a ductile and low shrinkage material. It develops sufficient bond strength, high compressive strength and less fluid loss comparing to OPC. However, studies showed some shortcomings of geopolymer, which should be enhanced to allow using the geopolymer in the oil field. The pumpability at elevated temperatures, for a certain period, is one of the current limitations of the geopolymer. Several experiments have been performed to get the proper compositions of the geopolymer and the appropriate retarding admixture, which help to increase the pumping time of the geopolymer paste. Chemical S&H revealed its potential to retard the setting time by 80 mins. It is proved that there many parameters, which control the setting time of the sample. The modular ratio, weight of the admixture and composition of the precursors, have an impact on delaying the thickening time. BS2 is more pumpability than BS1, and S7 is the sample which has the most significant pumping time among the others. Results from the uniaxial compressive test (UCS) and ultrasonic cement analyzer (UCA) show the compressive strength value is in an acceptable range for utilization in oil well cementing. Rheology properties of geopolymers were characterized as non-Newtonian shear-thinning fluid and its density within the permissible range (1.95 sg). These characteristics promote the geopolymer to be a good quality alternative material to be applied in downhole applications.

Author: Elias Plessing

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Carbon Capture and Storage (CCS) is essential for achieving carbon neutrality, especially in hard-to-decarbonize industries. One of the main challenges in CCS is ensuring that CO2 is permanently contained in geological storage sites. Cement is crucial for sealing the wellbore and preventing leaks. To evaluate durability of cement against CO2, traditional tests like API Specification RP 10 are used, which test cement in pressurized conditions and analyze its properties after exposure. However, these methods have their limits and new ways of testing are to be developed for more realistic results. This thesis consists of two parts. One is about the development of a new permeability testing setup to monitor the changes in permeability and strength of different types of cement that have been exposed to super-critical CO2 for 2 weeks, 4 weeks or not at all. The changes were significant and widely depending on what type of cement was used. The second part deals with the improvement of an experimental setup that has been developed to advance the evaluation of the interaction of cement with CO2. In this setup, cement slurry is placed in an annulus between a rock cylinder and metal. It is then exposed to CO2 radially through the rock. In this method a CT scanner is used to monitor the carbonation front in real-time. It measures CO2 consumption and makes it possible to implement new sensors such as ultrasonic. Furthermore, it provides immediate insights into cement integrity and the interactions between cement and CO2, thus enhancing the security of CO2 storage in CCS applications.

Author: Lukas Knechtl

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The mechanical strength of cement is a critical parameter for ensuring the integrity of the well. However, measuring this parameter within the wellbore is challenging, Consequently, the strength parameters are only obtainable on the surface before it is poured in place, or through simulative approaches within the laboratory. Therefore, the implementation of real-time monitoring systems to assess the cement strength would substantially enhance well safety and integrity concerns. The objective of this thesis is to improve the correlation between dynamic and static strength measurements. To that end, a precise methodology is proposed, and the execution of several testing procedures is undertaken. The results from these tests are then combined and summarized in a table. The studies methodology entails the establishment of a triaxial testing installation with integrated triaxial confining pressure recording, the adaptation of the sample preparation procedure according to the material equipment and the programming of a combination algorithm. The major objective, however, the was to find out an empirical relation between the triaxial compressive strength, the ultrasonic travel velocity, and the confining pressure, and to quantify them. Therefore, a series of cement slurries were selected and subjected to ultrasonic and triaxial testing for analysis. A total of six distinctive slurries were analyzed. These included a conventional class G cement (16 ppg), a bentonite slurry (12 ppg), a slurry containing hallow glass spheres (12 ppg), and two epoxy cement slurries (13.6 ppg), exhibiting varying rheological characteristics. Additionally, an epoxy slurry (12.9 ppg) containing ultrafine cement was examined. All samples were cast into one-time two-inch cylindrical samples and subsequently cured ambient conditions. Afterwards, ultrasonic pulse velocity analysis was conducted with piezoelectric sensors, followed by axially compressing the samples under triaxial conditions. To obtain detailed information about the deformation properties in the dimension of microstrain, samples were partially equipped with electrical strain gauges for varying confining pressures. Finally, all the acquired data was combined using a MATLAB algorithm, which resulted in a table with all important parameters of the different input slurries. The framework of this thesis includes crucial dynamic as well as static parameters like Poisson¿s ratio, Young¿s modulus, acoustic travel time, triaxial compressive strength, confining pressure as well as their deformation behavior and strain recordings. This investigation contains these parameters of 185 different cement samples from six distinctive slurries. This comprehensive dataset serves as a database and can be readily expanded for additional parameters derived from permeability tests or chemical exposure to materials such as CO2. Consequently, only some minor modifications are necessary in the combining algorithm. In essence, this research offers data-driven methodology for the assessment of the triaxial compressive strength, with the confining pressure and ultrasonic travel time serving as primary variables. This enables the assurance of structural integrity of wellbore cements, and therefore well integrity.

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Author: Marco Cavalli

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In view of global climate targets, the oil and gas industry faces the challenge of significantly reducing CO2 emissions, particularly in energy intensive processes, such as the operations performed by a German Well Service Company, for the workover of existing oilfields in Germany and Austria, especially heavy workover. These rigs consume a considerable quantity of fossil fuel every year which further leads to high CO2 emissions.
This thesis faces the problem of the high amount of emitted CO2 and analyses different methods which show, if there is a way to save emissions and applicability. The use of hydrogen (H2) as an alternative energy source, which is offering promising opportunities (on the one hand to reduce the amount of used fossil fuels and on the other hand to receive a cleaner combustion) to reduce the CO2 emissions and minimize the ecological footprint.

Another point for achieving this goal is to increase the efficiency and therefore optimize the engine performance. This is achieved by operating the motor at its best efficiency point (BEP), reducing specific energy consumption and CO2 emissions Any surplus in energy generated (in the difference of needed energy to the energy produced at BEP) can be stored in a battery, supercapacitors, kinetic or potential energy storages such as flywheels or gravitational storage options or used alternatively.
In addition to these techniques, the integration of photovoltaic (PV) systems is being analysed to cover all the energy requirements of the heavy workover systems with renewable energy sources. PV systems can be used for both direct power supply and for charging energy storage systems, further reducing the consumption of fossil fuels.
This thesis shows that the use of H2 injection, energy storage and integration of photovoltaic systems is a promising strategy for a significant reduction in CO₂ emissions resulting from heavy workover rigs. At the same time, the energy efficiency of the plants is increased, which gives an important contribution to the decarbonization of workover operations in the oil and gas industry.

Author: Alina Latysheva

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This study is devoted to improving Lessons Learnt reporting quality and procedures at OMV Well Engineering.
The first stage of the work was the analysis of informational support along the well engineering process. Types, capture, and transfer of drilling data were described for all well construction lifecycle phases. Reports were systematically categorized by introducing a four-digit coding, reflecting periodicity, data type, operation, and operation details. The analysis of current well construction reports identified shortcomings in the existing structure of the Lessons Learnt report.
The second step was to propose changes to the Lessons Learnt report structure to increase the effectiveness of the information collected. The distribution of non-productive time for OMV wells was analyzed, which identified drilling problem types. As an example, recommendations of improved Lessons Learnt reports were made for a particular type of problem.
The methodology of generating such a report was developed, which consisted of gathering meta-information and – depending on the type of drilling problem – various analyses of technical specifications and sensor data. The result of the procedure is a Lessons Learnt report, which is stored in a database that the drilling engineer uses in the well planning process during the offset well analysis phase.
In order to automate part of the process and reduce the human effort, a web-based application was created to extract non-productive time information from daily drilling reports or activities data.
In the final part of the work, the proposed methodology for creating the Lessons Learnt report was applied on a real well, and the results were successfully verified with historical data.

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Author: Felix Hibler

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Drilling operations and production facilities of the oil and gas industry are spread around the globe, also in remote locations, offshore or in the desert. In several cases, it is impossible to make the right component available at the right time to the right location, without enormous additional costs or effort. Manufacturing the required component to the exact specification directly at the location certainly adds huge benefits. Other industries such as automobile, aerospace have applied this just-in-time strategy very effectively by using the fast-developing additive manufacturing technologies. This thesis is embedded in an overall project which is performed by the Chair of Drilling and Completion Engineering together with OMV E&P GmbH. It investigates the usage of additive manufacturing in the oil and gas industry. The content of the thesis is divided into three main phases: testing of additive manufactured parts, an oil and gas specific SWOT-Analysis and a methodology describing the workflow for spare part manufacturing. During the first phase of the thesis the additive manufactured parts, which were produced from the selected material, 1.4542 (17-4 PH), are evaluated and compared to a conventionally manufactured part and the metal grade API C-110, which is a controlled yield strength casing or tubing grade. This phase includes the preparation of the specimens, testing and analysis of the results. The static behavior of the material in hardness, tensile and Charpy-V notch impact tests is evaluated. Sulfide stress cracking (SSC) and hydrogen-induced cracking (HIC) tests were conducted in an external lab. For the second phase a SWOT-Analysis is performed to evaluate the general opportunities and shortcomings of this manufacturing method, as well as the specific chances for embedding it into the supply chain of an oil and gas production or service company. During the third phase of the thesis, a methodology or workflow to produce an additive manufactured part is evaluated and established. The workflow starts at the point, where it is recognized that a specific component is needed at the rig or the production facility and ends when the manufactured part can be delivered to this location. Therefore, different methods are investigated and researched to create a 3D model where a blueprint may not be available for a variety of reasons. The main objectives of the thesis are to gain knowledge about the properties, particularities and limitations of additive manufactured parts, especially for the application in the oil and gas business. Furthermore, the benefits of integrating this technology in certain areas are shown, to get one step closer to a safe and efficient way to use it in the oil and gas industry.

Author: Karez Abdulhameed

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Cement integrity is a critical aspect of ensuring a reliable and sustainable life for a geothermal well, where compromising factors such as cycling thermal stress, corrosive formation fluids, and the formation's nature put the well integrity under a long-term test. The integration of fibre optic cable adds a significant advantage to monitoring the well in real-time; however, the installation within the cement sheath can locally disturb the microstructure, alter stress distribution, and potentially initiate microcracks and/or micro-annuli around the cable that threaten overall well integrity.
This work is aiming to evaluate whether the cement sheath integrity could be compromised by the presence of the fibre optic cable or not. And hence it investigates the coupled mechanical behaviour of geothermal well cement in the presence of embedded fibre optic cables through a combined experimental and numerical approaches including uniaxial compressive strength (UCS), N2 permeability, optical & digital microscopy, ultrasonic wave readings, indirect tensile strength test, post cutting posh-out bond test, and the FEA simulations as well as some mechanical calculations.

As to the methodology, after a successful preliminary manual bond check with 1-inch specimen, a simulation of strength tests was conducted to get the minimum specimen size for UCS tests with cable. This was found to be 2-inch diameter samples above which the perturbations caused by the installation of the cable can be ignored for the laboratory strength test purpose. 32 specimens, as well as two casing-cement-cable assemblies, were prepared corresponding to the two cement recipes, as well as destructive and non-destructive tests that were planned. An important point is that the idea of this thesis was quite novel, hence the author had to develop new approaches addressing the faced challenges. Cases in point were the optimum specimen size design, cutting the samples, casing with the least damage to the casing-cable-cement bond, and developing the FEA codes to simulate the UCS tests.

The results show that the presence of a permanently embedded fibre-optic cable in the cemented wellbore annulus does not compromise the bulk mechanical integrity of geothermal well cement when proper slurry formulation and curing conditions are applied. Destructive and non-destructive strength tests indicate that cement strength and stiffness are primarily governed by curing quality, with the Tail cement consistently outperforming the Lead cement. Ultrasonic pulse velocity measurements confirm the strength trend of Tail > Tail + Cable > Lead > Lead + Cable, while showing only minor reductions due to cable presence. In contrast, post-cutting investigations reveal that interface behaviour is highly sensitive to mechanically introduced damage: cutting and polishing induce significant stresses that cause partial or complete cement–cable debonding, particularly in the Lead cement. Despite this, the push-out tests (still post cutting) show that the Tail cement holds a residual cable–cement interaction nearly four times stronger than that of the Lead cement, even after bond degradation. Overall, the findings indicate that long-term integrity risks are governed by interface mechanics, thermal mismatch, and curing conditions rather than by inherent degradation of the cement matrix due to fibre-optic cable installation.

Author: Karlo Delmis

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The project's goal was to redesign a laboratory-scale drilling rig called MiniRig at the Department of Petroleum Engineering, Montanuniversität Leoben. Laboratory-scale drilling rigs are the most feasible way of doing drilling research. Most laboratory-scale drilling rigs are unique, but they all try to mimic real-world size rigs. The MiniRig's environment consists of many parts that have to work together. The new iteration of the MiniRig uses the previous iteration's control box, servo motor, and top drive. The MiniRig's digital hearth is hidden in its control box. The control box's hardware and control software had incomplete documentation before this project. The control box's hardware and control software were reverse-engineered to document and implement them with the new MiniRig's parts. New sensors were added to the MiniRig, resulting in a new programmable logic controller (PLC) hardware and software configuration. The servo motor, top drive, and sensors are all fitted on the new derrick. The control box's connectivity drawings were created in an electric diagram design software called QelectroTech and are presented in this thesis. Reading and understanding the connectivity diagrams is a must for new PLC programs. The updated PLC routines are described in this work. A new program was written for the MiniRig manual operation. The program is described in the thesis and commented in the PLC's programming software called Automation Studio. The project's outcome is a manually operable MiniRig, a description of the MiniRig's parts, and encountered issues and solutions are documented.

Author: Viacheslav Kobets

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Early detection of stuck pipe incidence in real-time will lead to reducing the downtime and costly corrective actions. Therefore, in the last decades, intensive efforts have been made to develop methods to identify the stuck pipes early symptoms. One of these methods is torque and drag (T&D) modeling. Despite numerous advantages, the modeling-based method has, nowadays, T&D modeling is not common because it requires real-time merge and contextual data of heterogeneous frequency and quality as well as recalibration. The alternative approach is to apply data-driven algorithms to solve real-time torque and drag issues. This approach can be judged to be more robust than the first because real-time drilling data can be used. Besides, the data-driven algorithm does not limit the number of input parameters. From this perspective, this thesis proposes a model based on a machine learning concept focused on real-time detecting the early signs of impending stuck pipe by real-time monitoring the pertinent surface drilling parameters. The newly proposed method uses machine learning linear regression algorithms to predict several parameters such as standpipe pressure, hook load, surface torque. The model can train from the data gained and adjust its performance automatically. The predicted parameters help the model to evaluate the behavior of real-time data. This comparison results in an alert level table for every predicted parameter. The alert level table allows the model to calculate stuck probability and generate an alarm when the probability exceeds the preliminary set limits. As a result, the model is suited to use real-time drilling operation data as input, calculate stuck pipe probability and notify the driller when the risk of stuck pipe is out of threshold and may be recognized as dangerous. The first part of the thesis provides an overview of the problem, the current thesis challenges, and objectives. The main machine learning algorithms and data-based approaches application for early stuck pipe sign detection are denoted in the second part of the thesis. Finally, the third part of the work covers the methodology of the proposed approach in detail. Two case studies of the approach implementation using real-time data are also presented here. In conclusion, the results of the work are presented and summarised. The features and shortcomings of the proposed approach are also discussed. The resulting model proves its ability to implement real-time data monitoring to avoid costly and time-consuming stuck pipe incidents.

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Author: Amro Al Hmoud

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Abstract Drilling technologies has been developing and evolving ever since the discovery of oil to the human kind. Many reasons encouraged this development, the vast investment and the time to come up and the slightest maturing of this field of science. One of the major yet simplest ways to have one step forward is the ability to use two or multiple technologies in purpose of mitigating each other’s flows and cons. Conventional drilling methods have been a blast to the world of drilling, yet, they have their share of flaws such as tripping in and out operations, pipe handling, and some of these flaws might lead to an actual risk of well control problems. Thus, it was a motive to innovate solutions to attenuate those limitations. Casing drilling technology became a solution for many of the conventional drilling methods imperfections such as narrowing down the tripping operations to the point of no tripping out post reaching the planned depth, which helped reducing time which usual many hours are spent on using conventional methods. As for managed pressure drilling technology, it has proven it benefits on many projects by achieving a safer, more efficient and cost effectiveness. Also, it gives the ability to closely monitor the well and better accuracy determining or detecting aberrations encountered, thus an enhanced response capability. In this case study, several mud losses in different depths varying between partial and complete mud loss, and also a premature casing seat and pipe stuck problem occurred. All combined lead to a major non-productive time which increased the overall time spent and the cost dramatically. This thesis will focus on implementing both managed pressure and casing drilling technologies since both technologies proved worldwide their applicability for overcoming the problems encountered in this case study, which conventional drilling method was used in. The well hydraulic analysis and economical assessment of new technologies are provided and eventually conclude the outcome of applying the managed pressure casing drilling together.

Author: Amro Al Hmoud

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Abstract Drilling technologies has been developing and evolving ever since the discovery of oil to the human kind. Many reasons encouraged this development, the vast investment and the time to come up and the slightest maturing of this field of science. One of the major yet simplest ways to have one step forward is the ability to use two or multiple technologies in purpose of mitigating each other’s flows and cons. Conventional drilling methods have been a blast to the world of drilling, yet, they have their share of flaws such as tripping in and out operations, pipe handling, and some of these flaws might lead to an actual risk of well control problems. Thus, it was a motive to innovate solutions to attenuate those limitations. Casing drilling technology became a solution for many of the conventional drilling methods imperfections such as narrowing down the tripping operations to the point of no tripping out post reaching the planned depth, which helped reducing time which usual many hours are spent on using conventional methods. As for managed pressure drilling technology, it has proven it benefits on many projects by achieving a safer, more efficient and cost effectiveness. Also, it gives the ability to closely monitor the well and better accuracy determining or detecting aberrations encountered, thus an enhanced response capability. In this case study, several mud losses in different depths varying between partial and complete mud loss, and also a premature casing seat and pipe stuck problem occurred. All combined lead to a major non-productive time which increased the overall time spent and the cost dramatically. This thesis will focus on implementing both managed pressure and casing drilling technologies since both technologies proved worldwide their applicability for overcoming the problems encountered in this case study, which conventional drilling method was used in. The well hydraulic analysis and economical assessment of new technologies are provided and eventually conclude the outcome of applying the managed pressure casing drilling together.

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Author: Julian Klaus Pflügl

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Mechanical stuck pipe events are one of the key technical challenges of the drilling industry and incidents usually lead to an enormous amount of non-productive time and costs. Most of these events show that they could have been avoided by an early reaction to possible sticking indications. To improve the reaction time and thereby the efficiency of future drilling operations and to reduce the mechanical stuck pipe related NPT, a state-of-the-art drilling simulator in combination with knowledge of industry experienced personnel gets used to design an interactive and realistic training case. To provide a detailed analysation of different types of mechanical stuck pipe issues, relevant technical literature and the available best practice solutions within the industry get summarised. Each type is reviewed for its symptoms, preventive actions and freeing procedures. Using eDrilling AS´s state-of-the-art drilling simulator software, a tailor-made mechanical stuck pipe training scenario based on theoretical data is designed and implemented into the simulator. A case-based best practice solution to complete the scenario successfully gets provided. Additionally, a handbook for the simulator and its user interfaces and a step-by-step guide for the development and implementation of a general training case is created. After the evaluation of the drilling simulator opportunities, mechanical sticking due to a dogleg was established as a training case. It was found out that this type will provide the most realistic and reliable result. Not any parameter can be varied within the simulator software due to certain limitations from the provider. Besides the development from a theoretical idea to the actual simulation code and the analysation of important drilling parameters related to mechanical sticking, essential parts of the coding files get explained. Moreover, it was found that mostly the freeing procedures and not the recommended reactions to prior indications get described in the literature. Therefore, a best practice summary for the training scenario including preventive measures and freeing procedures is created. The detailed description of the simulator software including a guide for every application and user interface is originated. What remains unsolved is the actual impact on the reaction improvement during a real stuck pipe scenario of people who practised this training case on the simulator compared to others. Therefore, carrying out a study about the impact of the training on the simulator is highly recommended as future work. This is the first interactive training case on the state-of-the-art eDrilling AS simulator which confronts engineers and operational personnel with mechanical stuck pipe issues. It allows the unique possibility to practise identifying crucial warning signs as wells as reacting appropriately to such events. It supports the transformation of trainees into highly qualified personnel. With the provided workflow description and software code, users are able to understand how to work with such a simulator and to design and implement new digital drilling-related training cases.

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Author: Hassan Aoun

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A laboratory-scale drilling rig, MiniRig, is being developed by the Chair of Drilling and Completion at DPE Leoben, represents a major step forward in the field of drilling technology. The rig is designed to provide a unique and innovative solution for drilling operations, with a sprocket-and-chain hoisting system that is different from the conventional hoisting systems used in other drilling rigs. The key aspect of the rig's operation is the hook load, which is determined by the readings from the four load cells that are attached to the traveling block, where two load cells are attached on each of the two chains. To improve the accuracy of the load cell readings, the configuration of the load cells was carefully manipulated through Automation Studio. By applying a strain gauge factor with a higher resolution, the calculations of the digital values of the load cells were much more precise, allowing for a more accurate calculation of the actual mass suspended on each load cell and the hook load. The resulting calculation of the hook load is affected by the friction forces that are encountered by the traveling block as it moves along the vertical shafts. In order to gain a deeper understanding of the MiniRig's traveling block and hook load dynamics, a series of experiments were conducted. These experiments included a study of the block position, incrementally adding weigh, movement of the traveling block, WOB (weight on bit) application, and examination of the effect of tension in the load cell connections. The results showed that the position and direction of the block affect the hook load readings, and the friction of the block on the vertical shafts can reduce the weight measurements. Furthermore, the tension in the load cell connections has a noticeable impact on the readings. With the outcomes of these experiments, the MiniRig has now reached an operational state, with a thorough understanding of its traveling block and hook load dynamics. This information will be valuable in performing a drill off test, which requires the activation of the drill motor and the connection of the circulation system. Additionally, the MiniRig can be utilized for educational purposes and, in the future, will be fully automated with the development of a theoretical operating envelope. With its unique design and innovative features, the MiniRig is poised to play an important role in the field of drilling and completion, providing a new and effective solution for drilling operations.

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Author: Yaroslav Kuprin

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Use of extended reach drilling (ERD) practices has become a common means to economically access reserves from existing infrastructure, provide the way to reserves that were previously out of reach, and reduce the environmental footprint of drilling and production facilities. Unfortunately, in industry there are still a lot of ERD wells that have been lost or made uneconomic by a lack of effective planning, especially planning of running casing into the lower intervals. Casing running normally takes only a small percentage of the well development life cycle. However, the consequences of failing to get the casing to section total depth are normally very significant of quality time in well planning. Thus, development of clear procedures and active management of this operation will usually give a high success rate. Within this master thesis an integrated approach to mitigate problems during casing the long 12-1/4 inch section with 9-5/8 inch liner in a new ERD well in Russian offshore field is suggested. Firstly, the analysis of common torque and drag, borehole cleaning, hydraulics and other challenges specific to casing running job are analyzed. Furthermore, there is an overview of the best practices and possible measures to overcome or prevent those issues. In the case study the experience of 4 ERD wells is presented and the whole process of liner running job in the planned well, including hole cleaning and setting of liner-top packer, is discussed.

Author: Clemens Peter Ettinger

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The transition to clean and sustainable energy is one of the top priorities in the modern world. Nowadays, the impacts of global warming are evident in almost every country across the globe, and world-leading companies are taking ambitious steps to curb climate change. One of the critical factors that trap heat in the atmosphere are greenhouse gases, where carbon dioxide (CO2) plays the dominant role. Significant amounts of CO2 are produced during the burning process of fossil fuels. Consequently, the primary CO2 emission cuts can be made in places where significant amounts of fossil fuels are burned. However, to be able to control and make improvements in CO2 emissions, the first step is to have reliable CO2 level measurements and estimations across various processes. Being Europe's leading independent natural gas and oil company with more than 120 years of experience as an operator, Wintershall Dea (WD) has ambitious sustainability goals towards decarbonization and is looking to use the best available technologies for the reduction of greenhouse gas emissions (GHG). The estimation/calculation of emissions being created by the company's activities is key in identifying solutions. As a part of this research, WD wants to analyze the company's carbon footprint in rigless intervention and well services activities for the existing operating assets. This research will be done in cooperation with the Global Well Construction team at Wintershall Dea in order to look for methods to accurately determine the amount of GHG emissions from the company's global rigless activities. This thesis aims to pioneer the work in seeking ways to define the amounts of GHG emissions precisely. The aim of this thesis is to understand how and where uncertainty does occur during the emission reporting for rigless well interventions. Followed by the development of a model which assesses the uncertainty and mitigates it for a better monitoring of greenhouse gas emissions. The created methodology can be used and implanted into the already established reporting process to report emissions more precisely.

Author: Fabian Fasching

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To ensure well integrity during carbon capture and storage (CCS) operations, it is essential to understand the effects of carbon dioxide (CO2) on the cement at high-pressure and temperature conditions. There are several providers of CO2-resistant types of cement for the oil and gas industry, promising the integrity of their products. However, there are no standardized testing procedures to test their cement. This thesis aims to create a new testing methodology for CO2-resistant cement types and to investigate the quality of a CO2-resistant cement using the proposed methodology. The new testing methodology uses two types of high-pressure vessels. Smaller autoclaves are used to condition cement specimens (2" height x 1" diameter) with CO2. These specimens are used to analyze the compressive strength, mineralogical composition, and inhomogeneities in the cement matrix at different conditioning stages. The second pressure vessel is the CT-Scannable CO2 Cell, in which the propagation of the carbonation front is measured using a medical CT scanner. By combing the results of both procedures, an estimation of the material's behavior under downhole conditions can be made. The results from this study can assist in the prevention of well integrity problems due to CO2 leakage, therefore mitigating health, safety, and environmental risks and increasing the efficiency and economic success of CCS projects.

Author: Anass Al Didi

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Cement plays an integral role in maintaining well integrity throughout the life cycle of a well. Successful cementing jobs provide good zonal isolation and ensure strong bonding of cement to the casing and formation. The cementing job success is mainly governed by the fluid displacement efficiency and the degree of contamination with other wellbore fluids. However, displacing fluids downhole over long distances is a complex task that requires understanding of mud-spacer-cement interactions, their rheological behavior, as well as frictional pressure losses and flow regimes. Computational Fluid Dynamics (CFD) has been proven to be a powerful tool for modelling fluid behavior in numerous industries. The use of CFD allows us to model these complexities in a precise and reliable manner, and it can provide tailored solutions for individual cementing jobs to ensure maximum job efficiency and safety. In this study, a state-of-the-art CFD model was created using Ansys Fluent software to examine the displacement efficiency of a cementing job under different conditions in eccentric annuli. The CFD model was validated in single phase simulations using two sets of experimental data. The parameters studied include fluid density and rheology, casing eccentricity, flow rate, wellbore deviation, and casing rotation. The effect of each parameter was analyzed and the data was compiled to provide guidelines for efficient fluid displacement. This study stressed the importance of maintaining density and viscosity hierarchies between the displacing and displaced fluids. The drastic effect of eccentricity on the displacement process was shown, as well as possible solutions to counteract this effect by optimizing fluid properties and flowrates. Furthermore, casing rotation proved to be a valuable tool that enhances the displacement efficiency and can partly mitigate the negative effects of high eccentricity. The CFD model proved to be an invaluable resource for optimizing the cement placement process and can be utilized in a variety of ways to provide specialized solutions for each cementing job.

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Author: Timothy Atkin

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In drilling, thus far, there have been several issues that may have significant impact on cement integrity that have not been fully understood. One of these issues is borehole ballooning. Borehole ballooning is sometimes referred to as breathing and is an expression used to describe the small volumetric change of the active fluid system, which might occur during the circulation of drilling fluids. At the present time, there has been limited research and inclusion of cementing to the bore hole ballooning challenge. With the increased amount of focus that comes with well integrity issues, accurate prediction of borehole ballooning while performing primary cement jobs becomes increasingly necessary to assure that the volumetric change and its effect on the cement/formation bond that this causes is correctly accounted for. In the context of the above challenges this thesis project aims to explore the utilisation of a numerical software model to study the effects of borehole ballooning that occurs while cementing on the cement integrity in terms of volumetric change, several scenarios are studied with three different types of cement and 3 different types of surrounding formation. Based on the results recommendations will be proposed, which may help to reduce risks and improve the cement operation. This thesis suggests that a somewhat small volume change over a relatively moderate section length, as indicated by the results, could mean that problems with the integrity of wells might not be as considerable as originally proposed. This small volume would be taken into account by existing quantities of cement or by changing the cement properties in a minor way to reduce the degree of deformation. The strength of the surrounding formations also provides support and limits the amount of deformation. The displacement velocity has the largest impact on the level of deformation, the marginal difference increases as the velocity increases but is still comparatively small.

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Author: Daniel Eisengschirr

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An accurate calculation of surge and swab pressures is of utmost importance as pressure changes during tripping are one of the leading causes of well control incidents. The thesis presents numerical investigations of swab and surge pressures in concentric and eccentric annuli. A series of concentric and eccentric simulation cases, mimicking a straight section of the wellbore, is defined. As a non-Newtonian incompressible drilling fluid, 1% polyanionic cellulose is selected. Tripping speeds range from 0.1 to 0.8 ft./s. Hexahedral and, in the case of complex geometries, polyhedral computational meshes are used. The numerical investigations are conducted with the solver pimpleFoam from the computational fluid dynamics (CFD) toolbox OpenFOAM® and post-processed with the software ParaView. The simulation results of different concentric cases are successfully validated with existing laboratory experiments. The thesis presents additional eccentric cases with pressure-reducing effects of up to 38% and the associated annular flow profiles. The effect of a linear drill string acceleration on the surge and swab pressure is shown. The impact of drill string rotation and a bottom-hole-assembly on the pressure behavior in the annulus as well as the occurrence of turbulence are discussed. Results of the numerical investigations are compared with an analytical swab and surge pressure model by Srivastav et al. and the model is extended for eccentric annuli by a correcting term based on the simulation results. The thesis presents an application of CFD to swab and surge pressure modeling. It states a novel analytical pressure model that allows the direct calculation of pressure changes in an eccentric annulus.

Author: Elias Johannes Benedikt

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Well Integrity is defined in two different ways. According to the standard NORSOK D-010, which defines the most widely accepted definition, well integrity means “Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well”. Another definition gives the ISO TS 16530-1: “Containment and the prevention of the escape of fluids (i.e. liquids or gases) to subterranean formation surfaces.” To prevent the escape of fluids it is crucial to maintain the integrity of the well throughout the whole life cycle of the well. By establishing and implementing a Well Integrity Management System (WIMS) the well operator has an efficient management tool to cover and ensure the different aspects of well integrity. To fulfil the objective a set of operational Key Performance Indicator (KPIs) help to measure the effectiveness and the development of the WIMS. Well Integrity Management requires a multidisciplinary approach thinking which leads to the integration of aspects such as risk management, monitoring, organizational structures etc. In this thesis, the local WIMS at Gas Nord of Wintershall Dea will be reviewed and an overview of the current aspects that are in place will be given. According to the 117 Norwegian guidelines O&G, the current risk categorization system at Gas North has associations with risk, however it is not an absolute measure of the total risk exposure of the well. This categorization system does not replace risk assessment. Therefore, a measurement tool for the risk exposure has to be developed. By having a closer look at the well construction, intervention and production history of the well through a performance assessment with a scorecard, the well operator is able to identify future problematic wells in terms of risk exposure. Well integrity events are not only linked to constraints in the well operation phase but also to shortcomings in the well construction and intervention phase . By means of scorecards, 11 wells will be evaluated not only based on the operation phase but also on basis of the well construction phase. The scoring results will help to predict probable weak points in the well that can cause future well integrity issues. Further possible correlations of current well integrity incidents with the scorecard evaluation results can be identified and analysed based on probable origins. This thesis will show a pathway on how to use the holistic approach for a risk assessment. The identification of the critical wells and well sections in a risk assessment will help to better predict and solve the well integrity issues before they are become a major risk.

Author: Mikail Seynaroev

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One of the severe failure events during drilling is the sticking of the drill string. That results in time loss for freeing the pipe and the risk of losing an expensive portion of tubular and equipment. Therefore, there is huge interest in applying predictive systems to avoid stuck pipe occurrences. Drilling time reduction and, after that, its cost reduction can be achieved when accident signs are detected in advance. An intelligent system, performing automatic analysis of the wells’ electronic passports of the specific field, warns the drilling crew about possible stuck events during drilling. Drilling accidents lead to prolonged, costly downtime and high financial costs for their elimination and liquidation. Early forecasting and prevention of complications is an essential and urgent task requiring modern engineering methods and approaches, for instance, machine learning algorithms. The research target presents an application of machine learning techniques, such as artificial neural network and random decision forest for stuck pipe prediction.

Author: Philipp Grasser

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The oil and gas industry, like many others, is facing challenges brought about by the energy transition, demanding the optimization of operations within defined boundaries. In terms of geo-energy exploration related activities, this is associated with a cost-effective and safe drilling operation. In this regard, it is crucial to minimize the occurrence of undesired downhole problems, which may delay the drilling process, potentially causing non-productive time. One of the essential keys to achieving that is the early detection of anomalous downhole behaviour by continuously monitoring the surface-measured drilling parameters. The hydraulic system, along with other key surface parameters, plays a crucial role in successful drilling operations. It not only facilitates the circulation of drilling fluids, hole cleaning, and bit colling, but also provides valuable insights of the current downhole condition. Accurate modelling and monitoring of the surface-measured standpipe pressure can serve as a reliable indicator of potential anomalous downhole behaviour. However, the conventional physics-based approach for modelling standpipe pressure faces limitation in accurately representing the dynamic and complex nature of the downhole condition. Regarding this issue, the ultimate goal of this thesis is to develop a data-driven model based on a machine learning concept to predict standpipe pressure with only three controllable surface parameters as input for the model and still provide robust estimates of the target variable. The models are trained with trouble-free drilling data, which should allow the model to represent the normal trend and thus provide means for analysis and trend identification by comparison of the actual value with the modelled values. In conclusion, the applied methodology and algorithm can provide acceptable estimates of the target variable utilizing minimum required datapoints stemming from the same well. However, an optimization of the applied approach can possibly lead to improved results. The provided confidence interval provides a range of possible values for the target variable, thus can be useful for analysis and real-time monitoring. However, the predicted confidence interval cannot be directly interpreted as a safe operation window.

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Author: Sven Curis

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In this thesis, the overview of the potential of carbon capture and storage projects is presented. As carbon dioxide is one of the main contributors to total greenhouse gas emissions, this could be a way to mitigate global greenhouse gas emissions in the future. The main problem of carbon dioxide injection is the carbonation process, which causes the increase of cement’s permeability and reduction of its compressive strength. This could ultimately lead to the loss of well integrity. One of the methods which could monitor the carbonation in real-time is the acoustic method. The sonic velocity of ultrasonic waves which go through a certain cement density is in correlation with its compressive strength. This is of a great importance as the compressive strength of the cement may be monitored with the acoustic method. This method is already widely applicable as the Ultrasonic Pulse Velocity method to determine the quality of the concrete. Together with the correlation, the crack investigation also took place to determine the depth of cracks and correlate them with sonic velocity. Finally, the overall experimental procedure with the necessary apparatus is presented in this thesis along with the results and steps which were so far made.

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Author: Elisabeth Csar

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Primary cementing is critical to zonal isolation and well integrity. Besides, cement plugs are used for several operations in the oil and gas industry, such as lost circulation control, formation testing, directional/sidetrack drilling, zonal isolation, and well abandonment. Set cement may be too soft or not in the planned location and hence fail to provide hydraulic seal and lead to well integrity and safety issues. This could be due to a number of issues, including contamination with wellbore fluids, ineffective displacement, and casing eccentricity. This thesis focuses on continuous monitoring real-time data during the hydration process of cement to be able to determine the phase of hydration process, to define the exact location of the cement, to establish contaminated parts of cement and prove a competent/imperfect well barrier. Electrical conductivity measurements could be an indication of how the cement slurry is hydrating and the degree of contamination. Several tests with different levels of mud contamination were performed and analyzed. In addition, experiments with fiber-optic sensoring to measure strain and temperature changes during cement slurry hydration were conducted. Both the electrical conductivity and fiber-optic measurements are able to identify degree of hydration and also level of contamination. The lab setup, test procedure, data, analysis, and results are presented and discussed. These measurements, analysis, and application would significantly improve the accuracy of cement jobs, and operational performance in the oil and gas industry. Benefits to the industry from continuous monitoring and evaluation are discussed. In addition, recommendations for future work and conclusions can be found in the last chapter of the thesis.

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Author: Paul Wagner

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Global warming is one of the most significant issues the world is facing. Capturing carbon dioxide from the atmosphere or industrial processes and storing it in geological formations can help counteract climate change. Nevertheless, the interaction between well barrier elements such as cement, casing, tubulars, packers, and valves can lead to possible leakages. To accomplish successful carbon dioxide sequestration, injecting the carbon dioxide in its supercritical state is necessary. The supercritical carbon dioxide can corrode steel and elastomers and react with the calcium compounds in the cement, dissolving them and forming calcium carbonate and bicarbonate in the process. This carbonation can lead to channels forming on the cement-to-rock interface or cracking due to the carbonate precipitation, resulting in a loss of well integrity. This study focusses on finding ways that enable the continuous monitoring of well integrity under in-situ conditions. The construction of an autoclave, capable of withstanding supercritical conditions of carbon dioxide, facilitates the in-situ monitoring. This autoclave also makes CT-scans of the pressurized sample possible, as well as acoustic measurements, using state-of-the-art piezo elements. The first tests will establish a baseline using neat Class G Portland cement to verify the design and sensors. The set up consists of a rock core in the middle of the autoclave cell surrounded by a cement sheath. Drilling a channel in the middle of the core expedites the distribution of the carbon dioxide. Once the ability of the sensors to monitor the integrity is verified, different cement compositions and their interaction with supercritical carbon dioxide can be studied. The experimental setup and the procedure discussed here closely simulate the downhole condition. Hence, the results obtained using this setup and procedure is representative of what could be observed downhole. The direction is not to remove the sample from the cell and analyze it under in-situ conditions. Digitalization is powering the in-situ analysis in this experiment. After the carbonation, samples from the autoclave undergo a thorough chemical and physical analysis. The correlation of the data from the sensors and chemical analysis aids in further developing real-time monitoring. The results from this study can lead to the prevention of leakage of carbon dioxide to the environment and other formations, which defeats the purpose of carbon dioxide sequestration. These results should improve the economics of these wells as well as the health, safety, and environmental aspects.

Author: Danila Samokhvalov

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The consumption of oil and gas worldwide continues to experience a dramatic increase. However, the era of "easy" resource extraction has already ended, and the production of oil and gas has become a more complex process. Petroleum engineers are searching for the most efficient methods to enhance existing technologies. Nonetheless, the high complexity of such projects results in increased costs and implementation risks. Managed Pressure Drilling (MPD) is an advanced drilling technique that enables precise control of the wellbore pressure profile during drilling operations. The advantages of applying MPD can significantly enhance well control issues and minimize many risks associated with drilling. Real-time downhole data measurements are a crucial component for improving MPD, enabling engineers to monitor wellbore pressure and adjust drilling parameters in real-time. The most promising technology that provides such capabilities today is Wired Drill Pipe (WDP) technology providing power and data supply from surface to downhole, implemented by an Austrian technology company. One of the most demonstrative aspects of the mutual application of MPD and this new downhole power and data transmission technology is the ability to prevent and mitigate kick incidents, which can lead to disastrous consequences such as a blowout without proper management. These two technologies are capable of reducing risks related to kick and blowout events, but the primary research interest is dedicated to examining the extent of their joint effectiveness in comparison with separate applications. To achieve this research objective, the overall advantages of the technologies and their safety barriers against kick incidents are examined in comparison with conventional and alternative practices. For quantitative estimation, the Probabilistic Risk Assessment (PRA) is conducted. The obtained results for collaborative application show that the probability of experiencing kicks and blowouts decreased by 23 and 97 times respectively. The synergetic effect, represented by the estimation of general benefits and quantitative risk assessment performed in this study, demonstrates the essential improvement in the safety and efficiency of the drilling process, justifying additional expenditures associated with the joint MPD and the downhole power and data technology utilization.

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Author: Andreas Liegenfeld

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Maintaining the integrity of a well throughout its whole life cycle is very crucial in well construction and operation. Many risks are waiting along that chain of events to threaten the well’s integrity. Recent studies and research have long tried to link well integrity events to constraints in the well operation phase, with emphasis on stresses and their limits in the cement sheath. However, this thesis aims to have a closer look at the well construction process and how it might impact well integrity events. Through a simple performance assessment of the well construction process, a score between 0 and 100 is assigned to each casing/liner section to asses wellbore quality. Responses and parameters during drilling, final BHA pull, casing-running and cementing were used as input for the scoring process. The performance assessment output of the scorecard is precious in detecting shortcomings in the well construction process to help determine root causes of well integrity events. The scoring results of 29 casing/liner sections on 11 OMV Vienna Basin wells already indicate the tool’s effectiveness in detecting problematic well sections. The lowest-scoring ones face incidents like failing casing pressure tests, proven lack of zonal isolation or cementing losses during cementing. Furthermore, the scorecard’s ability to trouble-shoot problematic well sections has been proved with actual and expected/calculated casing pressure test bleed-off volumes. Gaining knowledge about the performance of the well construction process helps to enhance wellbore quality and avoid future well integrity events. The proposed wellbore scorecard tool only covers and captures what is happening in the well construction process, but to study and understand well integrity along the whole life cycle of the well, a more holistic approach will be necessary. Therefore, a stress model is proposed to understand the impact of well operations on the cement sheath in terms of stresses and failure of the cement. Manufacturing a test cell according to the proposed design to verify the stress model is highly recommended. This piece of work covers one essential part of the holistic approach to better understand well integrity events and aims towards a more environmental-friendly, safer and cost-effective way to operate hydrocarbon wells.

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Author: Pouya Ziashahabi

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Well integrity is one of the main issues during all life cycles of the well and if any barrier element fails and compromises the integrity of well, remedial strategy may have to be performed to restore the safety and economics of the well. Cement is conventionally used as the isolation material in remedial and primary jobs. However, due to several inherent limitations in cement characteristics, such as cement shrinkage or poor cement slurry compatibility with downhole fluids, it is not always the best solution. Besides these, cement slurry is a particle laden fluid which prevents it penetrating in to tight cracks/pathways to ensure isolation during remedial treatments. This project illustrates the effort to develop a customized polymer as cement alternative and/or cement additive to address challenges posed by conventional cement. Experimental studies are designed to evaluate the characteristics such as rheology, injectivity and mechanical properties of the customized polymer. Furthermore, the compatibility of these polymers with drilling fluids contamination and shrinkage behaviour upon cure are evaluated. Afterward, based on the results of measurements, the limitations of each different formulation are determined and the best formulation is optimized. In addition, the application of the polymer as an additive to conventional cement is studied to optimize some specific properties, such as mechanical properties and permeability. The results of experiments prove that beside the appropriate rheological properties, the polymer provides excellent mechanical properties and much lower shrinkage rate upon cure compared to cement and other systems available in the market. The customized polymer withstands and maintains its properties after being contaminated with considerable volume of drilling fluids and its compressive strength is not much affected by contamination. Also, combination mixtures of customized polymer with conventional cement slurries provide enhanced properties, such as lower permeability and higher compressive strength. The unique characteristics of customized polymer as cement alternative could provide benefits to industry by solving several current challenges in achieving secure isolation. Particularly due to its ability to penetrate in to tight cracks, this customized polymer affords an effective method in to mitigate sustained casing pressure or as a remedial solution for casing leakages which would not be achieved easily by conventional methods.

Author: Aleksei Olkhovikov

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Nowadays, oil companies are trying to extract more and more information from already existing data. However, it is still done by operational or engineering personnel, and drilling lessons learned are not an exception. It may lead to the loss of some small lessons or even to the mistakes in data interpretation. That is why companies are attempting to digitize everything to eliminate human influence on most of the processes. The purpose of this work is to develop a concept for automatic lessons learned extraction from gathered data and giving recommendations to the drilling engineer based on them during a well design process. To achieve this goal, the concept of using machine learning algorithms to digitize the well design process was developed. Status quo of lessons learned capturing and analysis at OMV was investigated, and its downsides were found. Discovered problems may be solved by the implementation of a recently developed knowledge graph database because it has many benefits in comparison with standard databases. For instance, a comprehensive information search which returns not only documents that match sent query but also important information related to that document, therefore, a user does not have to look through the whole document to retrieve required data. Additionally, the knowledge graph database is capable of returning information from other documents which have a specific value of similarity with the uploaded one. Additionally, this work provides some prototypes of machine learning models for wells clustering based on its trajectories, lithologies and activities. Also, a simple OCR algorithm was coded to digitize PDF documents. The developed approach showed the applicability of machine learning algorithms to automatically capture lessons learned from already existing data and smartly apply them during the design of a new well.

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Author: Christian Scheurer

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Nanoparticles have gained close attention over the recent years in many industries but especially so in the oil and gas. Various researches have been investigating, for instance, the use of surface-modified silica nanoparticles in reservoir rock applications. In this work, the interaction of silica nanoparticles and sandstone rock was investigated using a combination of various experimental approaches. Among others, fluid-fluid and rock-fluid interactions were assessed by means of fluid compatibility, batch sorption experiments and single-phase core floods. The underlying task was to gain a better understanding on the factors influencing nanoparticle adsorption to the rock material. In the experimental approach, diol and polyethylenglycol (PEG) surface-modified silica nanoparticles were tested using two brines differing in ionic strength, plus sodium carbonate (Na2CO3) and Berea and Keuper outcrops (core plug and crushed form). Core flood effluents were analysed to define changes in concentration and a rocks retention compared to a tracer. Field Flow Fractionation (FFF) and Dynamic light scattering (DLS) in selected effluent samples were performed to investigate changes in size distribution. Adsorption was evaluated using UV-visible Spectroscopy and scanning electron microscopy (SEM). Highest adsorption was observed in brine with high ionic strength whereas the use of alkali reduced the adsorption. Crushed material from Berea rock showed slightly higher adsorption compared to Keuper rock whereas temperature had a minor effect on adsorption behaviour. In single phase core-flood experiments no effects on permeability have been observed. The used nanoparticles showed a delayed breakthrough compared to the tracer and bigger particles passed the rock core faster. Nanoparticle recovery was significantly low for PEG-modified nanoparticles in Berea, suggesting high adsorption. SEM images indicate, that adsorption spots are defined via surface roughness rather than mineral type. Despite an excess of nanoparticles in the porous medium monolayer adsorption was the prevailing type observed. Investigation of nanoparticle interactions with rocks required the development and improvement of methods to evaluate concentration history and recovery. The understanding obtained is crucial for further research in this area and application in a possible field trial.

Author: Ibrahim Abou Askar

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An integral cement sheath that allows zonal isolation is crucial for safe and economical Oil and Gas production throughout the life cycle of hydrocarbon wells. For an integral cement sheath to achieve its goal, both short- and long-term cement properties must be tailored using cement additives to accommodate various cementing applications and well operating conditions. Although various types of additives exist, the current trend in reducing the carbon footprint motivates developing “greener” additives that are environmentally friendly and made from renewable and sustainable sources. Cellulosic particles, Cellulose nanocrystals (CNC) in particular, fulfil these requirements as it is characterized by superior properties. Several studies have showed the significant impact CNC has on the cement slurry; however, the major1ity of these studies were intended for the construction industry while the topic of hydrocarbon and geothermal well cementing was not thoroughly addressed. Increased degree of hydration, flexural strength, tensile and compressive strength, reduction in and alteration of various cement properties are observed upon adding CNCs to the cement. The significant impact CNC has on the cement slurry and the lack of data on the topic drives the interest in investigating the use of CNC as a high-performance cement additive. From this perspective, the main goal of this thesis is to study the CNC influence on well cement using API standard equipment and testing procedures. Based on the experimental findings, CNCs were found to influence cement properties by different magnitudes. For instance, a significant reduction in free water and shrinkage as well as a significant improvement in both long-term compressive strength and early compressive strength development were observed. In addition, increasing CNC concentration caused an increase in cement viscosity where a shear thinning profile is observed from rheological measurements. On the other hand, minor influences were observed in thickening time and static fluid loss. The observed reduction in fluid loss is attributed to the increase in viscosity caused by the addition of CNCs. Finally, compressive strength and rheological measurements were utilized to determine the threshold of CNC agglomeration. The optimum CNC concentration was also determined based on the most significant observed improvements in tested properties.

Author: Anastasiia Fedorova

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Well abandonment is a major challenge in the industry from different perspectives, including costs, the amount of effort and technical difficulties involved with permanent wellbore isolation. In recent years there has been an increased focus on plug and abandonment (P&A) operations. Oil and gas producing companies have an enormous asset of wells to be decommissioned due to mature fields all over the world. The North Sea region is not an exception, as it is the mature play experiencing the wave of well decommissioning activity for the last 15 years.
In the North Sea area, nearly two thousand wells are intended to be plugged and abandoned in the upcoming 5-10 years. P&A of wells of North Sea assets is estimated to reach 50 % of decommissioning costs, including platform removals, which compromise 20 % (Vrålstad, et al. 2018). Operators are searching for new technologies that could minimize expenditures on P&A operations as there are no financial benefits from them.
Well abandonment must fulfil local government regulations, which require long-term well integrity and isolating formations between each other and from the surface. A conventional well decommissioning process might be time-consuming due to remedial cementing, casing milling and casing pulling operations with the rig installation.
The main objective of the master thesis is to investigate the ´shale-as-a-barrier´ (SAAB) technique as the alternative solution to conventional well barriers. Naturally occurring barriers may extend over hundreds of meters along the well and eliminate the need for additional sealing of the annulus. Such a technique could simplify the plugging operations and imply significant cost reductions during P&A operations.

Author: Borna Les

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Given the scale of oil and gas projects and the complexity of systems involved, it is evident that ramifications of poor wellbore execution can manifest throughout the whole well lifecycle. Minimizing these ramifications calls for proactive management of wellbore quality already during well construction. However, the term `wellbore quality¿ remains loosely defined in this context, although commonly associated with adherence to a certain time, conditions, and cost constraints. While numerous studies suggest a positive correlation between increased wellbore quality and drilling performance, proving this beyond a reasonable doubt remains challenging due to the complexity of the drilling environment. Nonetheless, improved downhole conditions are generally agreed to enhance the likelihood of meeting well objectives, through either improved operational sequences or drilling performance, establishing a presumed link between wellbore quality and downhole conditions. Many efforts have been undertaken so far to characterize or forecast downhole problems through data-driven and/or physics-based models, there is, to the author¿s knowledge, no established method for quantifying wellbore acceptability. To tackle this issue, this thesis introduces a data-driven framework designed to diagnose and quantify signs of compromised wellbore health, aiming to provide means of quantifying the degree of wellbore acceptability in real time. The study introduces a high-dimensional concept to monitor the drilling process¿s health by creating a healthy reference baseline, combining deep learning (DL) and readily available data-derived metrics. Much like medical diagnostics, drilling anomalies are interpreted as symptoms, and hypothesized to correlate with a deterioration of wellbore health, with their intensity and frequency seen as indicators of wellbore health deterioration. The measure of drilling conditions acceptability is proposed in the form of the wellbore health value metric referred to as the `Symptom severity¿ index. The proposed index aims to refine wellbore quality management during drilling by deepening insight into downhole conditions, thereby facilitating timely interventions and mitigating unwarranted remedial actions. Ultimately, the index is intended to optimize drilling process sequences, thus helping to conserve resources and minimize emissions associated with the well construction process.