Download or read book Interplay of Porous Media and Fracture Stimulation in Sedimentary Enhanced Geothermal Systems written by Caitlin Marcus Hartig and published by . This book was released on 2015 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fracture Propagation and Permeability Change Under Poro thermoelastic Loads Silica Reactivity in Enhanced Geothermal Systems written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Geothermal energy is recovered by circulating water through heat exchange areas within a hot rock mass. Geothermal reservoir rock masses generally consist of igneous and metamorphic rocks that have low matrix permeability. Therefore, cracks and fractures play a significant role in extraction of geothermal energy by providing the major pathways for fluid flow and heat exchange. Therefore, knowledge of the conditions leading to formation of fractures and fracture networks is of paramount importance. Furthermore, in the absence of natural fractures or adequate connectivity, artificial fractures are created in the reservoir using hydraulic fracturing. Multiple fractures are preferred because of the large size necessary when using only a single fracture. Although the basic idea is rather simple, hydraulic fracturing is a complex process involving interactions of high pressure fluid injections with a stressed hot rock mass, mechanical interaction of induced fractures with existing natural fractures, and the spatial and temporal variations of in-situ stress. As a result, it is necessary to develop tools that can be used to study these interactions as an integral part of a comprehensive approach to geothermal reservoir development, particularly enhanced geothermal systems. In response to this need we have developed advanced poro-thermo-chemo-mechanical fracture models for rock fracture research in support of EGS design. The fracture propagation models are based on a regular displacement discontinuity formulation. The fracture propagation studies include modeling interaction of induced fractures. In addition to the fracture propagation studies, two-dimensional solution algorithms have been developed and used to estimate the impact of pro-thermo-chemical processes on fracture permeability and reservoir pressure. Fracture permeability variation is studied using a coupled thermo-chemical model with quartz reaction kinetics. The model is applied to study quartz precipitation/dissolution, as well as the variation in fracture aperture and pressure. Also, a three-dimensional model of injection/extraction has been developed to consider the impact poro- and thermoelastic stresses on fracture slip and injection pressure. These investigations shed light on the processes involved in the observed phenomenon of injection pressure variation (e.g., in Coso), and allow the assessment of the potential of thermal and chemical stimulation strategies.

Download or read book Investigating Fracture Network Creation During Hydraulic Stimulation in Enhanced Geothermal Systems written by Ayaka Abe and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: During hydraulic stimulation treatment in an enhanced geothermal (EGS) reservoir, it has been suggested that a complex fracture network including both preexisting natural fractures and newly formed fractures is created. In this stimulation mechanism, a fracture propagating from a preexisting natural fracture and the interaction of newly formed fractures and preexisting natural fractures play an important role in the creation of a fracture network. Analyzing the interaction between preexisting fractures and newly formed fractures during hydraulic stimulation is thus necessary to understand the creation of a fracture network. We approached to this research question with laboratory and numerical experiments for an EGS reservoir where large preexisting fractures dominate. Laboratory scale hydraulic fracturing experiments were conducted to investigate how a fracture network is created when a propagating hydraulic fracture and a preexisting fracture interact. The physics-based numerical model developed in this work was used to investigate fracture network creation from a small scale area including a small number of fractures to a reservoir scale with tens of fractures. We analyzed the geological factors that affect the fracture network patterns through the laboratory and numerical experiments. We observed that the stress state and preexisting fracture orientation affect the fracture propagation pattern in the laboratory experiments. The numerical analysis shows that the stress field induced by an upstream hydraulic fracture causes asymmetric distributions of normal and shear stresses along the preexisting fracture when they intersect, which resulted in initiation of a wing crack from the fracture tip on the side with larger angles. The numerical results also showed that the complexity of the created fracture network is affected by the fracture intersection angle, stress state, and injection rates. We reviewed past EGS projects and analyzed the stimulation mechanism during their hydraulic stimulation treatment. This study implies that stimulating a reservoir with poorly oriented preexisting fractures may result a complex and broad shaped fracture network, which would be beneficial for energy recovery.

Download or read book Fracture Stimulation in Enhanced Geothermal Systems written by Mark W. McClure and published by . This book was released on 2009 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fractures in Geothermal Reservoirs written by Geothermal Resources Council and published by . This book was released on 1982 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rock Fractures and Fluid Flow written by National Research Council and published by National Academies Press. This book was released on 1996-08-27 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: Scientific understanding of fluid flow in rock fracturesâ€"a process underlying contemporary earth science problems from the search for petroleum to the controversy over nuclear waste storageâ€"has grown significantly in the past 20 years. This volume presents a comprehensive report on the state of the field, with an interdisciplinary viewpoint, case studies of fracture sites, illustrations, conclusions, and research recommendations. The book addresses these questions: How can fractures that are significant hydraulic conductors be identified, located, and characterized? How do flow and transport occur in fracture systems? How can changes in fracture systems be predicted and controlled? Among other topics, the committee provides a geomechanical understanding of fracture formation, reviews methods for detecting subsurface fractures, and looks at the use of hydraulic and tracer tests to investigate fluid flow. The volume examines the state of conceptual and mathematical modeling, and it provides a useful framework for understanding the complexity of fracture changes that occur during fluid pumping and other engineering practices. With a practical and multidisciplinary outlook, this volume will be welcomed by geologists, petroleum geologists, geoengineers, geophysicists, hydrologists, researchers, educators and students in these fields, and public officials involved in geological projects.

Download or read book Transient Permeability in Porous and Fractured Sandstones Mediated by Fluid rock Interactions written by Chaojie Cheng and published by . This book was released on 2021* with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the fluid transport properties of subsurface rocks is essential for a large number of geotechnical applications, such as hydrocarbon (oil/gas) exploitation, geological storage (CO2/fluids), and geothermal reservoir utilization. To date, the hydromechanically-dependent fluid flow patterns in porous media and single macroscopic rock fractures have received numerous investigations and are relatively well understood. In contrast, fluid-rock interactions, which may permanently affect rock permeability by reshaping the structure and changing connectivity of pore throats or fracture apertures, need to be further elaborated. This is of significant importance for improving the knowledge of the long-term evolution of rock transport properties and evaluating a reservoir' sustainability. The thesis focuses on geothermal energy utilization, e.g., seasonal heat storage in aquifers and enhanced geothermal systems, where single fluid flow in porous rocks and rock fracture networks under various pressure and temperature conditions ...

Download or read book Modeling of Non equilibrium Heat Transfer in a Fractured Porous Medium for Enhanced Geothermal Systems Applications written by and published by . This book was released on 2012 with total page 1 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Stimulation Response Relationships for Complex Fracture Systems in Enhanced Geothermal Reservoirs written by and published by . This book was released on 2011 with total page 1 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Heat Transfer Investigations for Optimal Harnessing of Enhanced Geothermal Systems written by Esuru Rita Okoroafor and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Enhanced Geothermal Systems (EGS) offer the opportunity of exploiting the vast energy resources contained in hot impermeable rocks. In such rocks, the natural flow capacity of the system may not be sufficient to support adequate geothermal applications until it is enhanced by opening up existing fractures and propagating new fractures. Cold fluid is injected into the reservoir to exploit the energy resource, whose permeability has been enhanced. The increased permeability allows the fluid to circulate through the opened fractures to production or extraction well(s), thereby capturing and transporting the heat contained in the hot impermeable rock for power generation. Accurate prediction of the thermal performance of EGS depends on an understanding of how the heat transport is affected by the presence of the fracture(s) -- the primary flow conduit of EGS. These fractures may have aperture variability that could create channels and alter flow paths, affecting the availability of surface area for heat transfer. The overall goal of this study was to understand the fracture topology, investigate how it can impact flow and heat transport, and demonstrate ways Enhanced Geothermal Systems can be harnessed to optimize thermal performance. To achieve the goal of this study, a systematic fracture characterization approach was used, and numerical simulation models were used to study the physical processes that govern the interaction between the fluid and the rock during heat extraction from Enhanced Geothermal Systems. Using variogram modeling and Sequential Gaussian Simulation method, fracture apertures representing actual fractures were generated for lab-scale and field-scale investigations. Fracture characterization metrics such as the Joint Roughness Coefficient (JRC) and Hurst exponent were used in analyzing the data. Geometric anisotropy was a vital character of the generated fracture aperture distributions, which was seen to originate from the process of shearing or slip. Flow and heat transport relative to the direction of fracture shear was studied, with the perpendicular flow configuration being perpendicular to the direction of fracture shear. In contrast, the parallel flow configuration had flow in the same direction as the fracture shear direction. It was demonstrated in this study that the flow wetted surface area had a direct and significant contribution to the amount of heat extracted. For the lab-scale fractures, the JRC confirmed geometric anisotropy of the fracture aperture and was seen to have a direct correlation with the flow contact area. The lower the difference in JRC values between the perpendicular and parallel flow configurations, the more flow contact area expected in the perpendicular flow direction, which will lead to more heat extracted from the rock. From the variogram model parameters, it was deduced that high geometric anisotropy results in high differences in thermal drawdown and consequently a high difference in energy extracted. The thermal performance appeared to be better in the perpendicular flow configuration with a ratio of 70:30 for the lab-scale fractures. For the field-scale fractures, it was seen that most of the fracture aperture distributions with a geometric anisotropy ratio of 2 had Hurst exponents of fracture surface aperture variability found in nature. For all the fracture aperture distributions analyzed for the field scale, the perpendicular flow configuration resulted in better thermal performance than the parallel flow configuration with a ratio of 58:42. Furthermore, for the geometric anisotropy ratio of 2, the ratio was 70:30. The perpendicular flow configuration had the injected fluid move through tortuous flow paths. These tortuous flow paths contributed to more fracture surface area being contacted by the flowing fluid, leading to an improved thermal performance in that flow configuration. Throughout this study, temperature-dependent viscosity was used. However, a section of this study investigated the impact of using a constant viscosity in the thermohydraulic model. It was seen that for fractures with smooth, uniform apertures, for all temperature ranges and at the operating conditions being modeled, there was no significant difference between using a constant viscosity or a temperature-dependent viscosity in modeling an Enhanced Geothermal System. However, for fractures with spatial variations, it was determined that modeling with a temperature-dependent viscosity was necessary, especially for systems with high differences in reservoir and injection temperatures, and for fractures with high correlation lengths. The impact of thermal stresses on heat extraction was also investigated. An analog Enhanced Geothermal System, the Altona Field Laboratory, was also studied for thermo-mechanical influences. It was found out that the injection of hot water into the cold rock resulted in thermal stress generation and reduction in the aperture but did not cause significant changes to the temperature profile due to the small volumetric flow rate through the system. Also, anisotropic aperture distributions were studied to determine the impact of thermoelasticity on the heat extraction of Enhanced Geothermal Systems. It was shown that when thermoelasticity is taken into consideration, the thermal drawdown could either be improved or deteriorated depending on the nature of the aperture distribution. The impact of fracture aperture variability was investigated for Enhanced Geothermal Systems using supercritical CO2 as working fluids. It was established that CO2 as an EGS working fluid would result in better heat extracted from the system if the fractures are considered smooth, which agrees with related studies. However, where there is spatial variation in the fracture aperture, channeling could be detrimental to CO2, especially at high fracture correlation lengths and high mass flow rates, due to the high mobility of CO2. The following are the main contributions from this study. First, it has been demonstrated that heat transport is affected by the geometric anisotropy of fracture surfaces. It was determined that in most cases, flowing perpendicular to the direction of shear or slip results in more heat extracted due to more contact of the fluid with the rock while moving through tortuous flow paths. Secondly, the conditions under which a constant viscosity can be used in modeling EGS were determined. If the fractures are known to be smooth, have low correlation lengths, or have distributed surface areas, a constant viscosity can be used in the model, especially if the difference between the reservoir temperature and the injection water temperature is small. However, for anisotropic fracture surfaces, surfaces with high correlations lengths or high tortuosity, and when the difference between the reservoir temperature and injection water temperature is large, the use of constant viscosity could result in significant computational errors from the actual. Thirdly, it has been shown that thermal drawdown could either be improved or deteriorate when thermoelasticity is considered. This finding is different from studies previous studies that have looked into coupling thermohydromechanical processes for fractures with spatial variations and suggests that Enhanced Geothermal Systems may benefit from thermal stimulation. Finally, this work shows the first comparison between CO2 and water at a field scale considering fracture aperture variability. Recommended future work includes modeling of vertical fractures with spatial variations in fracture aperture to investigate how convection may impact the current findings; considering multiple fractures with spatial variations in the fracture aperture; considering non-Darcy flow in the simulation models; coupling geomechanics with the study of CO2 on fractures with spatial variations, and developing proxy models that are quicker to perform the thermohydraulic and thermohydromechanical simulations.

Download or read book Designing Enhanced Geothermal and Hydraulic Fracturing Systems Based on Multiple Stages and Proppant written by Sogo Shiozawa and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report consists of two chapters. In the first chapter, designs of Enhanced Geothermal Systems (EGS) with horizontal wells, multiple stages, and proppant are discussed. In EGS, hydraulic stimulation is used to improve well productivity. EGS is typically performed in a nearly vertical well, in one stage, with no proppant. Horizontal wells, multiple stages, and proppant are not used because they are considered not necessary and/or technically infeasible. We found that an EGS design with multiple stages and proppant could give dramatically improved economic performance relative to current designs. We reviewed the literature in order to assess the technical viability of our proposed design. The proposed design would increase cost but deliver substantial improvements in flow rate (and revenue) per well. The second chapter describes a simulation study of proppant transport with Newtonian fluid in a fully three-dimensional hydraulic fracturing simulator, CFRAC. This model has capability to handle proppant settling due to gravity, proppant migration away from the fracture walls, and fracture closure. In the model, the conservation equations of fluid and proppant are sequentially solved in a first-order finite difference scheme. A special algorithm is applied to handle proppant packing due to fracture closure. Our simulation results show good agreement with results from other recently published proppant modeling studies. Sensitivity analysis was performed in order to investigate the effect fluid viscosity, proppant density, and proppant size. Finally, simulations of the tip-screen out (TSO) were performed.

Download or read book Discrete Fracture Network Modeling of Hydraulic Stimulation written by Mark W. McClure and published by Springer Science & Business Media. This book was released on 2013-06-15 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discrete Fracture Network Modeling of Hydraulic Stimulation describes the development and testing of a model that couples fluid-flow, deformation, friction weakening, and permeability evolution in large, complex two-dimensional discrete fracture networks. The model can be used to explore the behavior of hydraulic stimulation in settings where matrix permeability is low and preexisting fractures play an important role, such as Enhanced Geothermal Systems and gas shale. Used also to describe pure shear stimulation, mixed-mechanism stimulation, or pure opening-mode stimulation. A variety of novel techniques to ensure efficiency and realistic model behavior are implemented, and tested. The simulation methodology can also be used as an efficient method for directly solving quasistatic fracture contact problems. Results show how stresses induced by fracture deformation during stimulation directly impact the mechanism of propagation and the resulting fracture network.

Download or read book Fracture Characterization in Geothermal Reservoirs Using Time lapse Electric Potential Data written by Lilja Magnúsdóttir and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The configuration of fractures in a geothermal reservoir is central to the performance of the system. The interconnected fractures control the heat and mass transport in the reservoir and if the fluid reaches production wells before it is fully heated, unfavorable effects on energy production may result due to decreasing fluid enthalpies. Consequently, inappropriate placing of injection or production wells can lead to premature thermal breakthrough. Thus, fracture characterization in geothermal reservoirs is an important task in order to design the recovery strategy appropriately and increase the overall efficiency of the power production. This is true both in naturally fractured geothermal systems as well as in Enhanced Geothermal Systems (EGS) with man-made fractures produced by hydraulic stimulation. In this study, the aim was to estimate fracture connectivity in geothermal reservoirs using a conductive fluid injection and an inversion of time-lapse electric potential data. Discrete fracture networks were modeled and a flow simulator was used first to simulate the flow of a conductive tracer through the reservoirs. Then, the simulator was applied to solve the electric fields at each time step by utilizing the analogy between Ohm's law and Darcy's law. The electric potential difference between well-pairs drops as a conductive fluid fills fracture paths from the injector towards the producer. Therefore, the time-lapse electric potential data can be representative of the connectivity of the fracture network. Flow and electric simulations were performed on models of various fracture networks and inverse modeling was used to match reservoir models to other fracture networks in a library of networks by comparing the time-histories of the electric potential. Two fracture characterization indices were investigated for describing the character of the fractured reservoirs; the fractional connected area and the spatial fractal dimension. In most cases, the electrical potential approach was used successfully to estimate both the fractional connected area of the reservoirs and the spatial fractal dimension. The locations of the linked fracture sets were also predicted correctly. Next, the electric method was compared to using only the simple tracer return curves at the producers in the inverse analysis. The study showed that the fracture characterization indices were estimated somewhat better using the electric approach. The locations of connected areas in the predicted network were also in many cases incorrect when only the tracer return curves were used. The use of the electric approach to predict thermal return was investigated and compared to using just the simple tracer return curves. The electric approach predicted the thermal return curves relatively accurately. However, in some cases the tracer return gave a better estimation of the thermal behavior. The electric measurements are affected by both the time it takes for the conductive tracer to reach the production well, as well as the overall location of the connected areas. When only the tracer return curves are used in the inverse analysis, only the concentration of tracer at the producer is measured but there is a good correlation between the tracer breakthrough time and the thermal breakthrough times. Thus, the tracer return curves can predict the thermal return accurately but the overall location of fractures might not be predicted correctly. The electric data and the tracer return data were also used together in an inverse analysis to predict the thermal returns. The results were in some cases somewhat better than using only the tracer return curves or only the electric data. A different injection scheme was also tested for both approaches. The electric data characterized the overall fracture network better than the tracer return curves so when the well pattern was changed from what was used during the tracer and electric measurements, the electric approach predicted the new thermal return better. In addition, the thermal return was predicted considerably better using the electric approach when measurements over a shorter period of time were used in the inverse analysis. In addition to characterizing the fracture distribution better, the electric approach can give information about the conductive fluid flowing through the fracture network even before it has reached the production wells.

Download or read book Geothermal Reservoir Engineering written by Malcolm Alister Grant and published by Academic Press. This book was released on 2011-04-01 with total page 379 pages. Available in PDF, EPUB and Kindle. Book excerpt: As nations alike struggle to diversify and secure their power portfolios, geothermal energy, the essentially limitless heat emanating from the earth itself, is being harnessed at an unprecedented rate. For the last 25 years, engineers around the world tasked with taming this raw power have used Geothermal Reservoir Engineering as both a training manual and a professional reference. This long-awaited second edition of Geothermal Reservoir Engineering is a practical guide to the issues and tasks geothermal engineers encounter in the course of their daily jobs. The book focuses particularly on the evaluation of potential sites and provides detailed guidance on the field management of the power plants built on them. With over 100 pages of new material informed by the breakthroughs of the last 25 years, Geothermal Reservoir Engineering remains the only training tool and professional reference dedicated to advising both new and experienced geothermal reservoir engineers. - The only resource available to help geothermal professionals make smart choices in field site selection and reservoir management - Practical focus eschews theory and basics- getting right to the heart of the important issues encountered in the field - Updates include coverage of advances in EGS (enhanced geothermal systems), well stimulation, well modeling, extensive field histories and preparing data for reservoir simulation - Case studies provide cautionary tales and best practices that can only be imparted by a seasoned expert

Download or read book Hydraulic Fracture Mechanics written by Peter Valkó and published by . This book was released on 1995 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book explores the theoretical background of one of the most widespread activities in hydrocarbon wells, that of hydraulic fracturing. A comprehensive treatment of the basic phenomena includes: linear elasticity, stresses, fracture geometry and rheology. The diverse concepts of mechanics are integrated into a coherent description of hydraulic fracture propagation. The chapters in the book are cross-referenced throughout and the connections between the various phenomena are emphasized. The book offers readers a unique approach to the subject with the use of many numerical examples.

Download or read book Hydraulic Fracture Stimulation Treatments at East Mesa Well 58 30 written by Republic Geothermal Inc.; Maurer Engineering Inc.; Vetter Research; United States. Department of Energy; Geothermal Reservoir Well Stimulation Program (U.S.) and published by . This book was released on 1981 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Micro mechanical Aspects of Hydraulic Fracture Propagation and Proppant Flow and Transport for Stimulation of Enhanced Geothermal Systems written by Ingrid Tomac and published by . This book was released on 2014 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: