# Browsing by Subject "Drilling"

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Item Advanced data analytics for optimized drilling operations using surface and downhole data(2022-12-05) Ashari, Rahmat; Oort, Eric van; Ashok, Pradeepkumar, 1977-Show more Minimizing well construction cost continues to be a dominant performance motivator for operators who rely on subsurface energy. Drilling optimization is a primary approach that drilling engineers use to lower costs, and this can be achieved by focusing on two goals: maximizing rate of penetration (ROP) and minimizing non-productive time (NPT). With the advances in sensors and computational technologies, data-driven approaches have become increasingly popular to achieve these goals. Nonetheless, experiences reveal that many operators underutilize the values that can be derived from their data. This research study develops data analytics approaches that incorporate surface and downhole data from drilling operations. In particular, two topics were studied in detail: connection recipes and bit damage tracking. The first topic aimed to develop an optimum approach to execute drillstring connections –i.e., the “connection recipes”– that yields a minimum level of vibrations so as to prevent downhole tool failures. The second topic specifically concerns drill bits, where the goal is to develop a workflow to track the state of bit damage in real time. An actionable outcome from such a workflow is the construction of a pull bit criterion, which serves as a guideline for drillers to decide whether a trip out is necessary. The data analytics workflows presented in this study will equip engineers with the capabilities to not only standardize connection-making practices to prevent downhole tools failures, but also optimize drilling performance by real-time bit damage monitoring that further helps lower NPT. For the connection recipes project, the data studied presented several unfavorable practices relating to surface rotational speed and weight on bit promoting the occurrences of stick-slip events, whirling, and shocks when going back to bottom and going off-bottom. Based on these observations, safer connection practices were identified. For the bit damage tracking project, bit wear and tooth wear metrics were computed. When applied on historical real-time drilling data, they revealed trip outs that were conducted either too early or too late. Based on several case studies, a bit pull criterion was subsequently developed. The two projects leveraged surface and downhole drilling data to produce insights and workflows that are deployable in real-time for drilling optimization.Show more Item Application of statistical learning models to predict and optimize rate of penetration of drilling(2016-12) Hegde, Chiranth Manjunath; Gray, Kenneth E., Ph. D.Show more Modeling the rate of penetration of the drill bit has been essential to optimizing drilling operations. Optimization of drilling – a cost intensive operation in the oil and gas industry– is essential, especially during downturns in the oil and gas industry. This thesis evaluates the use of statistical learning models to predict and optimize ROP in drilling operations. Statistical Learning Models can range from simple models (linear regression) to complex models (random forests). A range of statistical learning models have been evaluated in this thesis in order to determine an optimum method for prediction of rate of penetration (ROP) in drilling. Linear techniques such as regression have been used to predict ROP. Special linear regression models such as lasso and ridge regression have been evaluated. Dimension reduction techniques like principal components regression are evaluated for ROP prediction. Non-linear algorithms like trees have been introduced to address the low accuracy of linear models. Trees suffer from low accuracy and high variance. Trees are bootstrapped and averaged to create the random forests algorithm. Random forests algorithm is a powerful algorithm which predicts ROP with high accuracy. A parametric study was used to determine the ideal training sets for ROP prediction. It was conclude that data within a formation forms the best training set for ROP prediction. Parametric analysis of the length of the training set revealed that 20% of the formation interval depth was enough to train an accurate predictor for ROP. The ROP model built using statistical learning models were then used as an equation to optimize ROP. An optimization algorithm was used to compute ideal values of input feature to improve ROP in the test set. Surface controllable input features were varied in an effort to improve ROP. ROP was improved to save a predicted total of 22 hours of active drilling time using this method. This thesis introduces statistical learning techniques for predicting and optimizing ROP during drilling. These methods use input data to model ROP. Input features (surface parameters which are controllable on the rig) are then changed to optimize ROP. This methodology can be utilized for reducing nonproductive time (NPT) in drilling, and applied to optimize drilling procedures.Show more Item Automated characterization of drilling fluid properties(2016-12) Sullivan, Gregory John; Oort, Eric van; Karimi, AliShow more Accurate measurement of drilling fluid properties is essential in order to optimize wellbore construction, and in particular to properly manage hydraulics. It becomes even more crucial during deepwater drilling when a narrow mud window is present which may require the use of more advanced drilling technologies such as Managed Pressure Drilling (MPD) and Dual Gradient Drilling (DGD). Operating these technologies properly requires the use of sophisticated hydraulic models that require accurate rheological information as input. However, a full mud check with determination of all relevant rheological parameters is usually only carried out once per day, and augmented with one or two partial checks in the 24-hour period. Such intermittent and unreliable measurements are unfortunately not sufficient to provide the required inputs for ‘real-time' hydraulic modeling and control. A more practical approach for a continuous, automated monitoring of the drilling fluid properties is therefore called for. The method used here is based on the pipe viscometer approach rather than the traditional rotational viscometer method. In addition to the fluid rheology, important inputs for hydraulic models, such as mud density, transition to turbulent flow (critical Reynolds number), and real-time friction factor for non-Newtonian drilling and completion fluids are also obtained using the pipe viscometer. A prototype of this equipment was constructed, tested, and fully automated at The University of Texas at Austin. The flow loop was tested with several weighted and unweighted mud systems. During the measurement process, the driving pump was ramped up and held intermittently at various flow rates to measure the laminar frictional pressure loss in the pipe section. The data thus obtained was analyzed by software that generated a flow curve and from it derived relevant mud rheological parameters using a suitable rheological model. It also proved possible to extend the test to the turbulent flow regime and obtain the ‘true' friction factor in real-time for each particular fluid, rather than relying on a limited number of correlations that quite often exhibit inaccurate results, particularly for the Yield Power Law (YPL) fluids. Several successful tests with different mud systems indicate the reliability and robustness of the proposed technique.Show more Item Design and development of an X-ray sensor to measure the density and flow rate of drilling fluids in high pressure lines(2018-12) Singhal, Vivek, Ph. D.; Oort, Eric van; Chen, Dongmei; Bovik, Alan C; Barr, Ronald E; DiCarlo, DavidShow more There is a need for advanced technology that can accurately measure the density and mass flow rate of drilling fluids at the high pressure well inlet in real-time. Current reliance on antiquated metering technologies such as the pressurized mud balance and the pump stroke counter to make these measurements greatly impedes our ability to accurately predict the near well bore pressure profile and measure the delta flow rate, which is one of the primary indicators for trouble events such as kicks or lost circulation. In order to address this gap in technology an X-ray sensor was developed to make real-time measurements at greater than 99% percent accuracy and 1 Hz measurement frequency. The X-ray sensor can measure the density of drilling fluids in the 8 ppg to 20 ppg range and with flow rates of up to 1200 gpm. These measurements are made using 320 kV/1500W polychromatic X-ray source, which is well within the range of readily available industrial X-ray tubes. In the past such measurements would require X-ray voltages that could only be achieved with linear accelerators thereby making the cost and size of equipment non-conducive to the drilling environment. However, recent advances in pipe manufacturing, particularly using a class of low density and high pressure materials known as carbon fiber reinforced polymers (CRPs) and, are now making it viable to re-visit relatively low cost X-rays systems for density and mass flowrate measurements. Windows constructed from CRPs allow us to bypass the high density carbon steel standpipe and make measurements at voltages that do not require a linear accelerator. In this paper we discuss the design and implementation of a CRP based X-ray sensor that is used to measure drilling mud density and mass flowrate at the high pressure well inlet.Show more Item Development and applications of a new system to analyze field data and compare rate of penetration (ROP) models(2015-08) Mattos de Salles Soares, Cesar; Gray, Kenneth E., Ph. D.; Daigle, Hugh CShow more Improvements in data acquisition technology have enhanced rate of penetration (ROP) modeling capabilities. Modern logging tools are able to record more complete drilling datasets at a higher frequency, allowing for better understanding of the many variables that affect the drilling process. ROP models published in literature simplify drilling rate formulations by combining complex drilling factors into model coefficients. The lithology dependence of ROP model coefficients, as well as the model's performance evaluated based on different types of rocks, is a topic explored throughout this project. A data analysis software developed in Microsoft Excel VBA, named ROPPlotter, provides ROP field data visualization and comparison of different ROP models. Userforms offer great flexibility in selecting different sections of the well and in highlighting lithology changes. The program accomplishes data filtering by detecting data outliers in the original dataset and excluding them for a more meaningful analysis. Then, VBA coding is applied in order to produce neat-looking plots automatically, overcoming Excel’s poor standard plot formatting. Excel Solver is employed in determining coefficients of six ROP models: Bingham (1964), Bourgoyne & Young (1974), Winters-Warren-Onyia Roller Bit (1987), Hareland Drag Bit (1994), Hareland Roller Bit (2010) and Motahhari PDC Bit (2010). By studying how these coefficients change with varying rock formations, valuable information about each model's behavior is obtained. Plots containing field data and ROP models, in addition to parsed data utilized in model calculations, can be saved for future analysis with the click of a button. ROPPlotter is useful in conducting case studies for industry, such as slow ROP in a section of the well or slide drilling. Furthermore, it provides a systematic way to assess ROP model performance and aims to quantify the lithology dependence of ROP models and their coefficients. This exercise provides a means of determining which ROP model works best for a specific field application. Later, by using an average value of model coefficients calculated for a certain field, optimal values of parameters controlled at the rig floor (weight-on-bit, rotary speed, flow rate) are determined for a future well to be drilled on the same pad.Show more Item Development of a multiphase flow simulator for drilling applications(2017-08) Calvache Mejia, Sebastian; Sepehrnoori, Kamy, 1951-; Ribeiro, Paulo RShow more Drilling, or gas kick, simulators are becoming prevalent in industry due to their ability to replicate wellbore conditions that are not feasible in a laboratory setting. This is becoming more desirable as deeper wells are being explored. One of the biggest dangers that could happen during drilling operations is the onset of a gas kick. This occurs when a zone in the formation whose pressure is higher than that of the wellbore is breached. This allows for the undesired influx of formation fluids into the wellbore. If left uncontrolled, it could develop into a blowout. Gas kick simulators allow for testing of procedures that could be used to contain kicks at such depths. Furthermore, the use of drilling simulators could provide more insight into other phenomena. These include wellbore breathing and fracture ballooning, that cause similar kick symptoms at the surface and lead to expensive misdiagnosis, and the dissolution of gas into oil based mud, which could delay the identification of a kick. This thesis investigates the development of the initial integration of a drilling simulator into UTWELL, the wellbore simulator program developed at The University of Texas at Austin, by implementing a gas kick module. The transport equations of mass and momentum conservation were discretized using a Semi-Implicit Homogeneous Method over a one dimensional staggered grid. The multiphase phenomena were modelled using a Drift Flux approach as opposed to a mechanistic, Two Fluid approach. This was due to increased stability of the solution and faster computation time, despite the risk of loosing accuracy. The simulator was successful at simulating single phase flows for fluids with distinct rheology models, and with wellbores with discontinuities in the geometry. When attempting to simulate the well control of a gas kick in water based mud, the results were mixed. Attempt at simulating a `Floating Mud Cap' method failed due to the simulator's inability to perform drainage functions that allow for the raising and lowering of the mud level in the wellbore. However, the simulator was successful at capturing the behaviour of the gas kick as it entered and migrated through the wellbore, matching literature results. The simulator was compared to experimental data gathered from a test well. Three different scenarios were tested: No Drillstring, Semi-Submerged Drillstring and Drillstring at the Bottom. In all three cases, there was a good match between the experimental and simulation results for the bottomhole and choke pressures. The pit gain was severely overestimated in the 'No Drillstring' and 'Semi-Submerged Drillstring Case', however this was due to a higher influx of simulated gas having entered the wellbore during simulations. The 'Drillstring at the Bottom' simulation matched well with all data and with other simulators. Recommendations included full integration and testing of a compositional model to simulate oil based mud cases, implementation of automatic choke control and special flux splitting techniques in the discretization in order to better handle pressure waves caused by discontinuities.Show more Item Drilling performance improvement : Brett and Millheim model adaptations for interaction effects and multiple learners(2012-08) Coddou, Ginny Anne; Groat, Charles G.; Jablonowski, Christopher J.Show more This work reviews concepts in drilling-based learning curves and proposes modifications to the Brett and Millheim learning curve model to enable its use for multiple learners and to characterize interaction effects between learners. Enabling the model’s use for multiple learning scenarios at once improves modeling efficiency. Interaction effects are present when learners improve from their own experience and the experience of those in close proximity to them. Quantifying interaction effects leads to a more complete understanding of performance improvement and enables more effective forecasting of drilling resources and expenditure requirements.Show more Item Estimation of temperature-dependent parameters using an integrated thermal and hydraulics simulator for drilling applications(2018-12-07) Fallah, AmirHossein; Chen, Dongmei, Ph. D.; Oort, Eric vanShow more Today, wells are being drilled under complex conditions with complex well geometries, under High-Pressure High-Temperature (HPHT) conditions, with risk of riser gas unloading in deepwater operations, while using Managed Pressure Drilling (MPD) techniques, etc., resulting in a clear need for comprehensive multi-phase hydraulics software to simulate these conditions. To address this need, a thermal model is developed and added to a previously developed multi-phase software package. The de-coupled thermal model is able to estimate the temperature in the drillstring and the annulus fluids, as well as the formation temperature adjacent to the well, using an advanced explicit finite volume approach integrated with a semi-implicit scheme used in the hydraulics model. The model solves the energy equation for the wellbore fluids, assuming that the gas and liquid phases are at the same temperature. Comprehensive thermal resistance networks are used to calculate the heat transfer between the annulus and drillstring fluids, the annulus fluid and the formation, and in the formation. For better accuracy, axial heat conduction in the drilling fluid and heat generation at the bit are accounted for. Results of the model are compared against the well-known Hasan and Kabir model and commercial software, showing a very good match for both steady-state and transient cases. To show the importance of accurate temperature estimations, offshore and onshore kick scenarios are simulated for different drilling fluids and kick control methods. Using a comprehensive heat transfer model, a user-friendly Graphical User Interface (GUI) and advanced numerical schemes makes this model a robust tool for estimation of the drilling fluid and the formation during complex well control applications. The developed model is able to estimate crucial parameters during complex conditions, such as the pressure and temperature profiles, increased pit gain and outflow during kicks, gas solubility and unloading at low pressures, and even temperature-dependent formation strength. The addition of the energy equation comes without loss of previous modeling capabilities of the hydraulics simulator, such as accounting for area discontinuity in the well and drillstring, non-Newtonian fluid rheology, MPD techniques, and arbitrary 3-D well trajectoriesShow more Item A first-principles directional drilling simulator for control design(2014-12) Leonard, Rebecca Leigh; Oort, Eric van; Pryor, Mitchell WayneShow more A directional drilling simulator was constructed using a re-formulation of first-principles classical mechanics in order to serve as a platform for advanced control design. Dedicated focus was placed on building a modular solution that would interface with an existing Supervisory Control And Data Acquisition (SCADA) architecture. Model complexity was restricted to include only the features required to make an immediate step change in tool face control performance through more accurate determination of torsional dead time and time constant values. Development of this simulator advanced the art of drilling automation by building a foundation upon which developers may design novel control schemes using big data gathered in the modern oilfield. This first-principles model is supported by theoretical formulation of equations of motion that capture fundamental behavior of the drill string during both rotary and slide drilling operations. Wellbore trajectory was interpolated between survey points using the Minimum Curvature Method, and a semi-soft-string drill string model was assumed. Equations of motion were derived using energy methods captured in both Hamiltonian and Lagrangian mechanics and solved using the finite-element method. Transient dynamic solutions were obtained using Newmark integration methods. A sensitivity analysis was conducted to determine which parameters played the most influential roles in dynamic drill string behavior for various operational scenarios and to what extent those parameters influenced torsional dead time and time constant calculations. The torsional time constant was chosen as a measure of correlation between case studies, due to the significant role this value plays in state-of-the-art tool face control algorithms. Simulation results were validated using field data collected from rigs using a SCADA system to operate in various shale plays in North America. Results from field tests were used to compare torsional time constant values calculated using manually-determined, simulation-based, and analytical methods and investigate directional drilling performance over a range of operational scenarios. Simulation-based time constant calculation results were consistently more accurate than analytically-determined values when compared to manually-tuned values. The first-principles directional drilling simulator developed for this study will be adopted by the existing SCADA system in order to standardize and improve slide drilling performance.Show more Item Improved regulatory oversight using real-time data monitoring technologies in the wake of Macondo(2014-08) Carter, Kyle Michael; Van Oort, EricShow more As shown by the Macondo blowout, a deepwater well control event can result in loss of life, harm to the environment, and significant damage to company and industry reputation. Consistent adherence to safety regulations is a recurring issue in deepwater well construction. The two federal entities responsible for offshore U.S. safety regulation are the Department of the Interior’s Bureau of Safety and Environmental Enforcement (BSEE) and the U.S. Coast Guard (USCG), with regulatory authorities that span well planning, drilling, completions, emergency evacuation, environmental response, etc. With such a wide range of rules these agencies are responsible for, safety compliance cannot be comprehensively verified with the current infrequency of on-site inspections. Offshore regulation and operational safety could be greatly improved through continuous remote real-time data monitoring. Many government agencies have adopted monitoring regimes dependent on real-time data for improved oversight (e.g. NASA Mission Control, USGS Earthquake Early Warning System, USCG Vessel Traffic Services, etc.). Appropriately, real-time data monitoring was either re-developed or introduced in the wake of catastrophic events within those sectors (e.g. Challenger, tsunamis, Exxon Valdez, etc.). Over recent decades, oil and gas operators have developed Real-Time Operations Centers (RTOCs) for continuous, pro-active operations oversight and remote interaction with on-site personnel. Commonly seen as collaborative hubs, RTOCs provide a central conduit for shared knowledge, experience, and improved decision-making, thus optimizing performance, reducing operational risk, and improving safety. In particular, RTOCs have been useful in identifying and mitigating potential well construction incidents that could have resulted in significant non-productive time and trouble cost. In this thesis, a comprehensive set of recommendations is made to BSEE and USCG to expand and improve their regulatory oversight activities through remote real-time data monitoring and application of emerging real-time technologies that aid in data acquisition and performance optimization for improved safety. Data sets and tools necessary for regulators to effectively monitor and regulate deepwater operations (Gulf of Mexico, Arctic, etc.) on a continuous basis are identified. Data from actual GOM field cases are used to support the recommendations. In addition, the case is made for the regulator to build a collaborative foundation with deepwater operators, academia and other stakeholders, through the employment of state-of-the-art knowledge management tools and techniques. This will allow the regulator to do “more with less”, in order to address the fast pace of activity expansion and technology adoption in deepwater well construction, while maximizing corporate knowledge and retention. Knowledge management provides a connection that can foster a truly collaborative relationship between regulators, industry, and non-governmental organizations with a common goal of safety assurance and without confusing lines of authority or responsibility. This solves several key issues for regulators with respect to having access to experience and technical know-how, by leveraging industry experts who would not normally have been inaccessible. On implementation of the proposed real-time and knowledge management technologies and workflows, a phased approach is advocated to be carried out under the auspices of the Center for Offshore Safety (COS) and/or the Offshore Energy Safety Institute (OESI). Academia can play an important role, particularly in early phases of the program, as a neutral playing ground where tools, techniques and workflows can be tried and tested before wider adoption takes place.Show more Item Improved torque and drag modeling using traditional and machine learning methods(2020-08-13) Oyedere, Mayowa Olugbenga; Gray, Kenneth E., Ph. D.; Foster, John T., Ph. D.; Daigle, Hugh; Millwater, Harry; Jones, JohnShow more During the drilling process, the drillstring inadvertently comes in contact with the wellbore generating frictional losses in the rotating moment (torque) and axial force (drag). These losses reduce the rotational power available at the drill bit, thus making adequate torque and drag modeling a critical piece in the drilling puzzle. The simplifying assumptions of the widely used soft-string model for torque and drag modeling make it less accurate for new complex well designs, creating the need for the use of the more robust stiff-string model. This first part of this dissertation focuses on a new approach to developing a stiff-string model that can be easily implemented for well planning. The stiff-string model addresses the pitfalls of the soft-string model by using cubic splines for its well-path trajectory. It solves the three coupled, non-linear ordinary differential equations that describe the motion of the drillstring at each survey point to account for the shear forces and bending stiffness. The stiff-string model is then applied to design four horizontal wells. Drilling Optimization has consistently generated research interest over the years because of the cost-saving benefits of improving drilling efficiency. Rate of penetration (ROP) and torque-on-bit (TOB) predictions have become critical to the successful drilling optimization efforts. The second part of this dissertation focuses on the prediction and optimization of TOB using five regression-based machine learning algorithms. TOB was modeled as a function of rotary speed (RPM), weight-on-bit (WOB), flow rate, pump pressure, and unconfined compressive strength (UCS). Three direct search optimization algorithms—Nelder Mead, differential evolution, and particle swarm optimization (PSO)—were used to optimize TOB. The final part of this dissertation introduces a novel approach to ROP and TOB prediction by modeling it as a classification problem with two regions (low and high ROP and TOB respectively) based on a user-defined threshold. Five different classification algorithms were implemented and compared using the area under curve (AUC) classification metric. Finally, a probability gradient tool was developed to help inform the drilling engineer on the best combination of WOB and RPM to yield the desired drilling performanceShow more Item Leak-off test (LOT) models combining wellbore and near-wellbore mechanical and thermal behaviors(2015-08) Gandomkar, Arjang; Gray, Kenneth E., Ph. D.; Daigle, Hugh CShow more Considerable efforts to model leak-off test (LOT) and leak-off behaviors have been carried out in the past. Altun presented a model to estimate leak-off volume by dividing the wellbore system into four sub-systems: mud compression, casing expansion, fluid leakage, and borehole expansion (Altun 2001). The volume response from each sub-system is then combined to represent the total volume pumped during a LOT. Most existing leak-off models do not account for mechanical behavior of cement and rock formations around the wellbore. While their compressibilities are small, the cement and rock formation volume changes can be significant. In this research, a mechanical expansion model has been developed, based on a linearly elastic, concentric cylinder theory developed by Norris (Norris 2003). The model is an extension of Lamé equations for multi concentric cylinders and assumes the horizontal stresses on the system’s boundary are applied equally in all directions, i.e., the horizontal, far-field stresses around the system are isotropic. The resulting model simulates the compound radial displacements of casing, cement, and formation along the cased hole, based on pressures inside the wellbore and in the far-field stress region. The volume generated from concentric cylinder expansion is then combined with Altun’s model to simulate the total volume pumped during a LOT. One use of the model is the estimation of minimum horizontal far field stress. Since the model consists of concentric cylinders, the pressure on the outside boundary can approximate the minimum horizontal far field stress, which in turn is related to overburden pressure. The pressure inside the most inner cylinder is calculated from known mud weight. With an initial estimation for the far field stress and iterative methods, the minimum horizontal stress can be estimated. The developed models were then applied to field LOT data from Gulf of Mexico. The results show that leak-off volume along the cased hole should be analyzed as a compound expansion of casing, cement, and formation.Show more Item Methods for mud motor failure prevention : stall detection and temperature advisory(2022-05-09) De Saint Germain, Alexandre; Oort, Eric vanShow more Mud motor failure should be avoided where possible and a lot of research has gone into understanding potential mitigation strategies. Previous research performed for the RAPID group at the University of Texas at Austin identified stalls as a leading cause for mud motor damage and failure, yet very little research has been done to investigate them. Temperature is known to be leading factor in reducing mud motor life and will likely be more important now than it was in the past as drilling operations increase in complexity. In this work, we present two different algorithms designed to run while drilling. The first is a statistics-based stall detection algorithm designed to run on surface data. Where stall detection has previously based itself only on the Differential Pressure, our approach requires three simultaneous peaks in MSE, WOB and Differential Pressure. The second is a temperature model for the estimation of bottomhole temperature which can serve as a real-time advisory alerting if the temperature exceeds the motor rating. Both could be implemented in a damage index for the estimation of mud motor degradation at any timeShow more Item Numerical investigation of lost circulation and fracture resistance enhancement mechanism(2016-08-11) Zhao, Peidong; Gray, Kenneth E. Ph. D.; Santana, Claudia LShow more Drilling in complex geological settings often possesses significant risk for unplanned events that potentially intensify the economic problem of cost-demanding operations. Lost circulation, a major challenge in well construction operations, refers to the loss of drilling fluid into formation during drilling operations. Over years of research effort and field practices, wellbore strengthening techniques have been successfully applied in the field to mitigate lost circulation and have proved effective in extending the drilling mud weight margin to access undrillable formations. In fact, wellbore strengthening contributes additional resistance to fractures so that an equivalent circulating density higher than the conventionally estimated fracture gradient can be exerted on the wellbore. Therefore, wellbore strengthening techniques artificially elevate the upper limit of the mud weight window. Wellbore strengthening techniques have seen profound advancement in the last 20 years. Several proposed wellbore strengthening models have contributed considerable knowledge for the drilling community to mitigate lost circulation. However, in each of these models, wellbore strengthening is uniquely explained as a different concept, with supporting mathematical models, experimental validation, and field best practices. Due to simplifications of the mathematical models, the limited scale of experiments, and insufficient validation of field observations, investigating the fundamental mechanisms of wellbore strengthening has been an active and controversial topic within the industry. Nevertheless, lost circulation is undoubtedly induced by tensile failure or reopening of natural fractures when excessive wellbore pressure appears. In this thesis, a fully coupled hydraulic fracturing model is developed using Abaqus Standard. By implementing this numerical model, an extensive parametric study on lost circulation is performed to investigate mechanical behaviors of the wellbore and the induced fracture under various rock properties and bottomhole conditions. Based on the fracture analysis, a novel approach to simulate the fracture sealing effect of wellbore strengthening is developed, along with a workflow quantifying fracture gradient extension for drilling operations. A case study on fracture sealing is performed to investigate the role of sealing permeability and sealing length. The results described in this thesis indicate the feasibility of hoop stress enhancement, detail the mechanism of fracture resistance enhancement, and provide insights for lost circulation mitigation and wellbore strengthening treatment.Show more Item Patterns of weathering in sedimentary bedrock across a sequence of repeating ridges and valleys(2020-05-14) Pedrazas Hinojosa, Michelle Alexandra; Rempe, Daniella M.Show more Bedrock weathering plays a fundamental role in liberating nutrients, generating porosity, and producing soil. Compared to the mobile soil layer, little is known about the structure of bedrock weathering profiles across hillslopes and the extent to which observations from one hillslope can be scaled to represent other hillslopes of similar topographic form. Here, we compare patterns of bedrock weathering and water storage across a sequence of repeating ridges and valleys in the upturned sedimentary Great Valley Sequence of the eastern Northern California Coast Range. Deep drilling, downhole logging, and analysis of recovered samples reveal a common upslope thickening weathering profile across a sequence of ridges and valleys. The maximum weathering thickness at the divide is comparable across hillslopes with a nearly two-fold difference in hillslope length, suggesting that the thickness of weathering may not scale with hillslope dimensions. Within channels that bound hillslopes, bedrock cores are relatively unweathered within centimeters of the ground surface, while at ridges, the depth to the base of bedrock that is pervasively fractured and oxidized is about 7 m. Relative to fresh bedrock, matrix chips near the top of the weathered profile at the ridges have increased porosity by roughly 10% and experienced chemical denudation mass loss of 5 - 10%. Our observations reveal a pervasively weathered and fractured layer, which coincides with the oxidation front and is accompanied by unsaturated dynamic water storage. We show how hillslopes sharing the same lithology, vegetation, climate, and tectonic history also share patterns of bedrock weathering. Our data provide constraints on the mechanisms that couple the evolution of the land surface and the propagation of weathering fronts.Show more Item ROP in horizontal shale wells : field measurements, model comparisons, and statistical learning predictions(2015-08) Wallace, Scott Pine; Gray, Kenneth E., Ph. D.; Daigle, HughShow more Rate of Penetration (ROP) is one of the most important indicators of drilling efficiency available to drillers and engineers. Optimizing the ROP on a well allows the operator to decrease the amount of time spent drilling, which reduces cost. Further reductions in cost can come from utilizing and accurate performance model to understand whether a trip to the surface for a new bit is necessary, or if a bit trip would just increase Non Productive Time (NPT) without significantly benefitting performance. Clearly, understanding the factors that affect ROP is an essential part of drilling a successful well. Models for ROP have been developed over the academic history of Petroleum Engineering. One of the first models was the model developed by Bingham (1964), which offered a simple formula relating the RPM, Weight on Bit (WOB), and the diameter of the bit to a calculated value of ROP. Further work has continued in ROP modeling by Bourgoyne and Young (1974), who created a much more detailed ROP model including eight input parameters, Hareland and Rampersad (1994), who developed a drag‐bit specific model, and Motahhari et al. (2010), who developed a model specific to wells drilled with a positive displacement motor (PDM) and a polycrystalline diamond compact (PDC) bit. These models have a varying number of input parameters, and each rely on the tuning of between three and eight empirical coefficients in order to optimize them to the well which is being studied. This study applies these traditional ROP models to data collected while drilling modern horizontal shale wells. These wells were drilled with a rotary steerable system, as well as a downhole PDM, and PDC bit. The traditional models were first fit to the drilling data by using the full range of the horizontal section of the well to optimize the empirical coefficients. This method resulted in the traditional models acting largely like a moving average of the drilling performance over the horizontal region. Then, the empirical coefficients were optimized based on 50 ft sections of the horizontal region, which produced a much tighter fit between the calculated and actual ROPs. However this fitting methodology was found to be erroneous, since it was generating a forced overfit of the model to the actual data. Finally, the Wider Windows Statistical Learning Model was applied to the drilling data. This produced the best fits of any of the models which were considered, and was the only one of the models which followed the high‐frequency changes in the actual ROP data. As a result, this was the only one of the models which could be considered accurate for not only the estimation, but also the prediction and optimization of ROP in horizontal shale wells.Show more Item Testing geologic and geometric effects on drilling operations using torque and drag models(2015-12) Ho, Anthony, M.S. in Engineering; Gray, Kenneth E., Ph. D.; Daigle, HughShow more Intuitively, geologic and geometric effects on torque and drag should be significant. But literature suggests otherwise. Lesage et al. (1988) wrote that friction coefficients are not affected by lithology and hole angle, among other things. And if friction coefficients are similar for all of these factors, then only inclination, azimuth, and pipe specifications affect torque and drag. My thesis looks to test this statement using Johancsik’s torque and drag model and data provided by our sponsors. Johancsik’s model was chosen to test these effects because it is the most widely used torque and drag model in industry. Johancsik’s model also only relies on surface data in order to conduct an analysis. This contributes to the widespread use of Johancsik’s model and therefore increases the applicability of this paper. Once Johancsik’s model was chosen, it became natural to choose the minimum curvature method to interpolate the wellbore trajectory because Johancsik’s model was designed using the minimum-curvature method. Also, the minimum curvature method is the most widely used wellbore-interpolation method in industry. By using the minimum curvature method, this paper increases its applicability to industry. The analyses were conducted by examining the friction coefficients of each individual formation and lithology and geometric section. Friction factors encompass all factors that are not explicitly captured by the model and any factors affecting torque and drag that are not in the model will be captured by the friction factors. This study found lithology effects to affect drag consistently, though more data is needed. Drag friction factors were consistent by lithology, though they did appeared less predictable in Dataset 1 than the Datasets 2 and 3. Lithology affected torque less consistently than it did drag, though again more data is needed. Again, the results from Dataset 1 appeared to differ from Datasets 2 and 3. Further analyses are needed to conclude if this is caused by factors unrelated to lithology or individual geologies. The geometric effects of curved versus straight sections appear to not affect torque and drag. The results from the curved sections from the analyses have little relation to each other. As for more specific geometries, more analyses are needed before conclusions can be reached.Show more Item Thermal modeling for calculation of formation temperatures for deep water wells with chemical heat source(2015-12) Incedalip, Oguz; Oort, Eric van; Espinoza, David NicolasShow more Drilling through depleted zones is becoming more common as the resources are exhausted and the fields mature. To be able to access deeper sections of the reservoirs, it is essential to drill through depleted zones effectively. This need brings around the challenges including severe lost circulation and poor zonal isolation. Artificially strengthening the wellbore is of crucial importance in order to achieve successful drilling as well as cementing for deep water wells. Altering the thermal stresses results in increased tangential stresses in the vicinity of the wellbore and therefore increases the fracture gradient. Thermal stresses can be increased through a controlled exothermic chemical reaction of certain salts which are coated via pharmaceutical techniques to delay the reaction until the carrier fluid transports the materials to the target zone. This approach with its innovative method surpasses other methods like downhole heaters as it is more practically feasible. The technique has a great potential to decrease mud losses, hence to decrease non-productive cost and time. In this study a computational thermal model is developed in order to calculate the temperature distribution of the formation as well as the annular and tubular fluids for given heat generation rates. The numerical model which uses finite volume techniques is developed for an axisymmetric cylindrical geometry including the drilling fluid, casing, annulus, and formation for transient heat transfer including a time and location dependent heat generation source. The results are analyzed in comparison to one analytical solution as well as a commercial software package, Drill Bench, in order to verify the accuracy of the model for scenarios with no heat generation, since modelling of heat generation is not available for the other approaches. Some parameters of the model such as the heat transfer coefficient are calibrated in order to achieve the best agreement between different analyses. Heat generation rates are obtained for different chemical compounds tested in insulated calorimeter experiments. The results of different heat generation rates for different heat generation durations as well other problem parameters such as circulation rate are investigated. In addition, thermal stress calculations based on the temperature increase are also presented.Show more Item Thermoporoelastic wellbore stability model with local thermal non-equilibrium(2018-12) Gandomkar, Arjang; Gray, Kenneth E., Ph. D.; Daigle , Hugh; Jones, John; Olson, Jon; Millwater, Harry; Montoya , ArturoShow more Wellbore stability is a key challenge for the exploration and production industry since it adds a great deal of additional cost. Traditional wellbore stability models such as elastic and poroelastic models are not sufficient in modeling the stability and produce erroneous results since they consider an isothermal condition. The industry also overlooks the potential impact of thermal effects on wellbore stability and utilizes a trivial approach in modeling the thermal stresses. During the drilling phase, the drilling fluid temperature is different from the formation temperature due to geothermal gradient and circulation of the mud inside the wellbore. Therefore, the assumption of an isothermal condition will not predict the correct wellbore stability condition, especially for high pressure and high temperature wells. The knowledge of in-situ stresses, breakout, and breakdown is vital to oil and gas industry, affecting wellbore stability, well location, production rate, completion and casing designs. Determination of breakout pressure helps avoid wellbore enlargement and shear failure, while, breakdown pressure aids in knowledge of the formation fracture gradient and the limits for the drilling mud weight window. Estimations of breakout and breakdown gradients can substantially be affected by the induced thermal stresses that occur during the drilling phase of a wellbore. The fully coupled thermoporoelastic model developed in this dissertation reveals the importance of induced thermal stress in stress resolution and wellbore stability evaluation. It produces reasonable results compared to uncoupled models and models with isothermal assumption. Most existing thermoporoelastic models utilize the assumption of local thermal equilibrium. The local thermal equilibrium assumption ignores additional pore and thermal stresses in the porous medium caused by temperature variations of the fluid and solid phases. This dissertation investigates the effect of thermal stresses on stress resolution around a wellbore and wellbore stability in a fully coupled condition with consideration of local thermal non-equilibrium heat transfer. The model is applicable for any wellbore trajectories in low and high permeable formations with consideration of conductive and convective heat transfersShow more