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Evidence Of Pressure Dependent Permeability In Long Term Shale Gas Production And Pressure Transient Responses
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Book Synopsis Evidence of Pressure Dependent Permeability in Long-Term Shale Gas Production and Pressure Transient Responses by : Fabian Elias Vera Rosales
Download or read book Evidence of Pressure Dependent Permeability in Long-Term Shale Gas Production and Pressure Transient Responses written by Fabian Elias Vera Rosales and published by . This book was released on 2013 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt: The current state of shale gas reservoir dynamics demands understanding long-term production, and existing models that address important parameters like fracture half-length, permeability, and stimulated shale volume assume constant permeability. Petroleum geologists suggest that observed steep declining rates may involve pressure-dependent permeability (PDP). This study accounts for PDP in three potential shale media: the shale matrix, the existing natural fractures, and the created hydraulic fractures. Sensitivity studies comparing expected long-term rate and pressure production behavior with and without PDP show that these two are distinct when presented as a sequence of coupled build-up rate-normalized pressure (BU-RNP) and its logarithmic derivative, making PDP a recognizable trend. Pressure and rate field data demonstrate evidence of PDP only in Horn River and Haynesville but not in Fayetteville shale. While the presence of PDP did not seem to impact the long term recovery forecast, it is possible to determine whether the observed behavior relates to change in hydraulic fracture conductivity or to change in fracture network permeability. As well, it provides insight on whether apparent fracture networks relate to an existing natural fracture network in the shale or to a fracture network induced during hydraulic fracturing. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148240
Book Synopsis Pressure Transient Analysis and Production Analysis for New Albany Shale Gas Wells by : Bo Song
Download or read book Pressure Transient Analysis and Production Analysis for New Albany Shale Gas Wells written by Bo Song and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Shale gas has become increasingly important to United States energy supply. During recent decades, the mechanisms of shale gas storage and transport were gradually recognized. Gas desorption was also realized and quantitatively described. Models and approaches special for estimating rate decline and recovery of shale gas wells were developed. As the strategy of the horizontal well with multiple transverse fractures (MTFHW) was discovered and its significance to economic shale gas production was understood, rate decline and pressure transient analysis models for this type of well were developed to reveal the well behavior. In this thesis, we considered a 0́Triple-porosity/Dual-permeability0́+ model and performed sensitivity studies to understand long term pressure drawdown behavior of MTFHWs. A key observation from this study is that the early linear flow regime before interfracture interference gives a relationship between summed fracture half-length and permeability, from which we can estimate either when the other is known. We studied the impact of gas desorption on the time when the pressure perturbation caused by production from adjacent transference fractures (fracture interference time) and programmed an empirical method to calculate a time shift that can be used to qualify the gas desorption impact on long term production behavior. We focused on the field case Well A in New Albany Shale. We estimated the EUR for 33 wells, including Well A, using an existing analysis approach. We applied a unified BU-RNP method to process the one-year production/pressure transient data and performed PTA to the resulting virtual constant-rate pressure drawdown. Production analysis was performed meanwhile. Diagnosis plots for PTA and RNP analysis revealed that only the early linear flow regime was visible in the data, and permeability was estimated both from a model match and from the relationship between fracture half-length and permeability. Considering gas desorption, the fracture interference will occur only after several centuries. Based on this result, we recommend a well design strategy to increase the gas recovery factor by decreasing the facture spacing. The higher EUR of Well A compared to the vertical wells encourages drilling more MTFHWs in New Albany Shale.
Book Synopsis Effects of Pressure-dependent Natural-fracture Permeability on Shale-gas Well Production by : Younki Cho
Download or read book Effects of Pressure-dependent Natural-fracture Permeability on Shale-gas Well Production written by Younki Cho and published by . This book was released on 2012 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Unconventional Reservoir Geomechanics by : Mark D. Zoback
Download or read book Unconventional Reservoir Geomechanics written by Mark D. Zoback and published by Cambridge University Press. This book was released on 2019-05-16 with total page 495 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive overview of the key geologic, geomechanical and engineering principles that govern the development of unconventional oil and gas reservoirs. Covering hydrocarbon-bearing formations, horizontal drilling, reservoir seismology and environmental impacts, this is an invaluable resource for geologists, geophysicists and reservoir engineers.
Book Synopsis Multiscale Analysis of Mechanical and Transport Properties in Shale Gas Reservoirs by : Mohammad Hatami
Download or read book Multiscale Analysis of Mechanical and Transport Properties in Shale Gas Reservoirs written by Mohammad Hatami and published by . This book was released on 2021 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation focuses on multiscale analysis in shale to improve understanding of mechanical and transport properties in shale gas reservoirs. Laboratory measurements of the effects of constant confining pressure (CCP), and constant effective stress (CES) on permeability were coupled with multiscale finite element simulations and the development of a comprehensive apparent permeability model to study the mechanical behavior of shale and transport mechanisms in shale. Predicting long-term production from gas shale reservoirs is a challenging task due to changes in effective stress and permeability during gas production. Unlike coal, the variation of sorbing gas permeability with pore pressure in shale does not always feature a biphasic trend under a constant confining pressure. The present contribution demonstrates that the biphasic dependence of permeability on pore pressure depends on a number of physical and geometrical factors, each with a distinct impact on gas permeability. This includes pore size, adsorption isotherm, and the variation of gas viscosity with pore pressure.
Book Synopsis Unconventional Shale Gas Development by : Rouzbeh G. Moghanloo
Download or read book Unconventional Shale Gas Development written by Rouzbeh G. Moghanloo and published by Gulf Professional Publishing. This book was released on 2022-02-23 with total page 498 pages. Available in PDF, EPUB and Kindle. Book excerpt: Unconventional Shale Gas Development: Lessons Learned gives engineers the latest research developments and practical applications in today’s operations. Comprised of both academic and corporate contributors, a balanced critical review on technologies utilized are covered. Environmental topics are presented, including produced water management and sustainable operations in gas systems. Machine learning applications, well integrity and economic challenges are also covered to get the engineer up-to-speed. With its critical elements, case studies, history plot visuals and flow charts, the book delivers a critical reference to get today’s petroleum engineers updated on the latest research and applications surrounding shale gas systems. Bridges the gap between the latest research developments and practical applications through case studies and workflow charts Helps readers understand the latest developments from the balanced viewpoint of academic and corporate contributors Considers environmental and sustainable operations in shale gas systems, including produced water management
Book Synopsis Integrative Understanding of Shale Gas Reservoirs by : Kun Sang Lee
Download or read book Integrative Understanding of Shale Gas Reservoirs written by Kun Sang Lee and published by Springer. This book was released on 2016-02-10 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This timely book begins with an overview of shale gas reservoir features such as natural fracture systems, multi-fractured horizontal wells, adsorption/desorption of methane, and non-linear flow within the reservoir. Geomechanical modelling, an aspect of importance in ultra-low permeability reservoirs, is also presented in detail. Taking these complex features of shale reservoirs into account, the authors develop a numerical model, which is verified with field data using the history matching technique. Based on this model, the pressure transient and production characteristics of a fractured horizontal well in a shale gas reservoir are analysed with respect to reservoir and fracture properties. Methods for the estimation of shale properties are also detailed. Minifrac tests, rate transient tests (RTA), and type curve matching are used to estimate the initial pressure, permeability, and fracture half-length. Lastly, future technologies such as the technique of injecting CO2 into shale reservoirs are presented. The book will be of interest to industrial practitioners, as well as to academics and graduate students in the field of reservoir engineering.
Book Synopsis Pressure Transient Testing by : John Lee
Download or read book Pressure Transient Testing written by John Lee and published by . This book was released on 2003 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pressure Transient Testing presents the fundamentals of pressure-transient test analysis and design in clear, simple language and explains the theoretical bases of commercial well-test-analysis software. Test-analysis techniques are illustrated with complete and clearly written examples. Additional exercises for classroom or individual practice are provided. With its focus on physical processes and mathematical interpretation, this book appeals to all levels of engineers who want to understand how modern approaches work. Pressure transient test analysis is a mature technology in petroleum engineering; even so, it continues to evolve. Because of the developments in this technology since the last SPE textbook devoted to transient testing was published, we concluded that students could benefit from a textbook approach to the subject that includes a representative sampling of the more important fundamentals and applications. We deliberately distinguish between a textbook approach, which stresses understanding through numerous examples and exercises dealing with selected fundamentals and applications, and a monograph approach, which attempts to summarize the state-of-the-art in the technology. Computational methods that transient test analysts use have gone through a revolution since most existing texts on the subject were written. Most calculations are now done with commercial software or by spreadsheets or proprietary software developed by users to meet personal needs and objectives. These advances in software have greatly increased productivity in this technology, but they also have contributed to a "black box" approach to test analysis. In this text, we attempt to explain what's in the box, and we do not include a number of the modern tools that enhance individual engineer productivity. We hope, instead, to provide understanding so that the student can use the commercial software with greater appreciation and so that the student can read monographs and papers on transient testing with greater appreciation for the context of the subject. Accordingly, this text is but an introduction to the vast field of pressure transient test analysis.
Book Synopsis Laboratory Estimation and Modeling of Apparent Permeability for Ultra-Tight Anthracite and Shale Matrix by : Yi Wang
Download or read book Laboratory Estimation and Modeling of Apparent Permeability for Ultra-Tight Anthracite and Shale Matrix written by Yi Wang and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Gas production from unconventional reservoirs such as gas shale and coalbed methane (CBM) has become a major source of clean energy in the United States. Reservoir apparent permeability is a critical and controlling parameter for the predictions of shale gas and coalbed methane (CBM) productions. Shale matrix and tight anthracite are characterized by ultra-tight pore structure and low permeability at micro- and nano-scale with gas molecules stored by adsorption. Gas transport in shale and anthracite matrices no longer always falls into the continuum flow regime described by Darcys law, rather a considerable portion of transport is sporadic and irregular due to the mean free path of gas is comparable to the prevailing pore scale. Therefore, gas transport in both anthracite and shale will be a complicated nonlinear multi-mechanistic process. A multi-mechanistic flow process is always happening during shale gas and CBM production, including Darcy viscous flow, slip flow, transition flow and Knudsen diffusion and their proportional contributions to apparent permeability are constantly changing with continuous reservoir depletion. The complexity of the gas storage and flow mechanisms in ultra-fine pore structure is diverse and makes it more difficult to predict the matrix permeability and gas deliverability. In this study, a multi-mechanistic apparent-permeability model for unconventional reservoir rocks (shale and anthracite) was derived under different stress boundary conditions (constant-stress and uniaxial-strain). The proposed model incorporates the pressure-dependent weighting coefficients to separate the contributions of Knudsen diffusion and Darcy flow on matrix permeability. A combination of both permeability components was coupled with pressure-dependent weighting coefficients. A stressstrain relationships for a linear elastic gas-desorbing porous medium under hydrostatic stress condition was derived from thermal-elastic equations and can be incorporated into the Darcian flow component, serving for the permeability data under hydrostatic stress. The modeled results well agree with anthracite and shale sample permeability measured data.In this study, laboratory measurements of gas apparent permeability were conducted on coal and shale samples for both helium and CO2 injection/depletion under different stress conditions. At low pressure under constant stress condition, CO2 permeability enhancement due to sorption-induced matrix shrinkage effect is significant, which can be either clearly observed from the pulse-decay pressure response curves or the data reduced by Cui et al.s method. CO2 apparent permeability can be higher than He at pressure higher than 1000 psi, which may be resulted from limited shale adsorption capacity. Helium permeability is more sensitive to the variation of Terzaghi effective stress than CO2 and it is independent of pore pressure. The true effective stress coefficient can be found two values at low pressure region (500 psi) and high pressure region (500 psi). The negative value indicates Knudsen diffusion and slip flow effect have more impact on apparent permeability than Terzaghi stress at low pressure. Additionally, laboratory measurements of gas sorption, Knudsen diffusion coefficient and coal deformation were conducted to break down the key effects that influence gas permeability evolution. Adsorption isotherms of crushed anthracite coal samples was measured using Gibbs adsorption principle at different gas pressures. The adsorption isotherm result showed that the adsorption capacity at low pressure changes with a higher rate and thus brings a significant sorption-induced rock matrix swelling/shrinkage effect. And the isotherm data are important inputs for the Darcy permeability models. The latter was coupled in the apparent-permeability model as the Darcy flow component which involves the sorption-induced strain component. Diffusion coefficients of the pulverized samples were estimated by using the particle method and was used to calculate the effective Knudsen permeability. The Knudsen diffusion flow component in the proposed apparent-permeability model was constructed by transforming Knudsen mass flux into permeability term and used to match the effective Knudsen permeability based on diffusion data. Increasing trends for all results were performed during pressure drop down in the result plots. And the modeling result showed very good agreements with them, giving a solid proof of the availability of Knudsen diffusion component as part of the proposed model. The results of a series of experimental measurements of coal deformation with gas injection and depletion revealed that the coal sorption induced deformation exhibits anisotropy, with larger deformation in direction perpendicular to bedding than those parallel to the bedding planes. The deformation of coal is reversible for helium and methane with injection/depletion, but not for CO2. Based on the modeling results, it was found that application of isotropic deformation in permeability model can overestimate the permeability loss compared to anisotropic deformation. This demonstrates that the anisotropic coal deformation should be considered to predict the permeability behavior of CBM as well as CO2 sequestration/ECBM projects.
Book Synopsis Effect of Pressure-dependent Permeability on Tight Gas Wells by : Mariela Franquet Barbara
Download or read book Effect of Pressure-dependent Permeability on Tight Gas Wells written by Mariela Franquet Barbara and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Tight gas reservoirs are those reservoirs where the matrix has a low permeability range (k
Book Synopsis Prediction of Boundary-dominated Flow for Low Permeability Reservoirs Using Early-transient Data by : Yuzhe Cai
Download or read book Prediction of Boundary-dominated Flow for Low Permeability Reservoirs Using Early-transient Data written by Yuzhe Cai and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Unconventional natural gas resources have become an important energy supply in North America. Shale gas and tight gas provides over half of the natural gas production in the United States. Linear flow is the most common flow type in tight and shale gas reservoirs. A density-based analytical approach was proposed by Vardcharragosad and Ayala (2014) that could predict well production performance in the linear flow regime. However, this approach requires reservoir and fluid properties for the prediction. As matter of fact, most of these reservoir properties are unknown and undetermined. The thrust of this study is to predict the long-term (Boundary-dominated period) well production behavior with the reservoir properties as inputs through an updated density-based approach.The BDF model proposed in this study is based on Vardcharragosad and Ayalas density-based approach (2015). A novel and key task for the BDF production prediction is the utilization of historical production data, which is often termed as Production Data Analysis (PDA). A PDA technique is used to estimate the characterization ratio, which is applied to replace reservoir properties in the prediction model. In addition, transition time needs to be determined to estimate reservoir size because it determines the starting point of the boundary-dominated flow. By using the estimated characterization ratio and the transition time, the novel density-based approach could be re-constructed without inputting specific reservoir properties. The proposed model was initially validated with numerical simulation results.This thesis presents a method to predict boundary-dominated flow behavior in tight and shale gas reservoirs without the knowledge of reservoir properties. The proposed transition time determination approach shows advantages over traditional end of half slope method. Thus, original gas in place can be directly calculated from results of transition time determination and early data analysis more accurately. Also, cost of techniques on determining reservoir properties such as well logging could be reduced.
Book Synopsis Stress-dependent Permeability on Tight Gas Reservoirs by : Cesar Alexander Rodriguez
Download or read book Stress-dependent Permeability on Tight Gas Reservoirs written by Cesar Alexander Rodriguez and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: People in the oil and gas industry sometimes do not consider pressure-dependent permeability in reservoir performance calculations. It basically happens due to lack of lab data to determine level of dependency. This thesis attempts to evaluate the error introduced in calculations when a constant permeability is assumed in tight gas reservoir. It is desired to determine how accurate are conventional pressure analysis calculations when the reservoir has a strong pressure-dependent permeability. The analysis considers the error due to effects of permeability and skin factor. Also included is the error associated when calculating Original Gas in Place in the reservoir. The mathematical model considers analytical and numerical solutions of radial and linear flow of gas through porous media. The model includes both the conventional method, which assumes a constant permeability (pressure-independent), and a numerical method that incorporates a pressure-dependent permeability. Analysis focuses on different levels of pressure draw down in a well located in the center of a homogeneous reservoir considering two types of flow field geometries: radial and linear. Two different producing control modes for the producer well are considered: constant rate and constant bottom hole pressure. Methodology consists of simulated tight gas well production with k(p) included. Then, we analyze results as though k(p) effects were ignored and finally, observe errors in determining permeability (k) and skin factor (s). Additionally, we calculate pore volume and OGIP in the reservoir. Analysis demonstrates that incorporation of pressure- dependence of permeability k(p) is critical in order to avoid inference of erroneous values of permeability, skin factor and OGIP from well test analysis of tight gas reservoirs. Estimation of these parameters depends on draw down in the reservoir. The great impact of permeability, skin factor and OGIP calculations are useful in business decisions and profitability for the oil company. Miscalculation of permeability and skin factor can lead to wrong decisions regarding well stimulation, which reduces well profitability. In most cases the OGIP calculated is underestimated. Calculated values are lower than the correct value. It can be taken as an advantage if we consider that additional gas wells and reserves would be incorporated in the exploitation plan.
Book Synopsis Pressure Transient Analysis of Shale Gas Reservoirs with Horizontal Boreholes by : Xuwei Zhong
Download or read book Pressure Transient Analysis of Shale Gas Reservoirs with Horizontal Boreholes written by Xuwei Zhong and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In common oil and gas industry, obtaining reservoir properties is critical to field development. Well testing has been one of the important tools to estimate reservoir characteristics such as permeability and reservoir thickness. The purpose of this study is to develop an expert system that can estimate reservoir characteristics based on constant flow rate pressure transient data from horizontal wells located in shale gas reservoirs.A commercial compositional reservoir simulator CMG-GEM was used in this study. An isotropic square reservoir model with one lateral well at the center was built. The model utilized stimulated reservoir volume (SRV) approach to represent the fractured zone of the reservoir. The SRV zone was more prolific than the rest of the reservoir due to its higher permeability and smaller fracture spacing. 37 x 37 reservoir blocks configuration was selected to use in the model after performing a grid block sensitivity analysis. Since this study requires training of the expert system, large number of data need to be generated. 15 reservoir and well completion parameters were selected as variables in specified ranges. Several MATLAB scripts were created to randomize the input variables and to build thousands of simulation models. The pressure transient data were collected in a numerical table after each model ran.The expert systems included seven Artificial Neural Networks (ANN). The ANNs were all generated by using MATLAB ANN Toolbox. The ANNs were classified into forward ANN and inverse ANN. The forward ANN was able to predict pressure transient data, while the inverse ANN was capable of predicting reservoir properties.During the final stage of this study, five graphical user interfaces (GUI) were developed. The GUIs allow the user to input required parameters, and to view results in numerical and graphical formats.
Book Synopsis New Advances in Shale Gas Reservoir Analysis Using Water Flowback Data by : Ahmad Alkouh
Download or read book New Advances in Shale Gas Reservoir Analysis Using Water Flowback Data written by Ahmad Alkouh and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Shale gas reservoirs with multistage hydraulic fractures are commonly characterized by analyzing long-term gas production data, but water flowback data is usually not included in the analysis. However, this work shows there can be benefits to including post-frac water flowback and long-term water production data in well analysis. In addition, field data indicate that only 10-40% of the frac water is recovered after the flowback. This work addresses two main question: Where is the rest of the injected frac fluid that is not recovered and what is the mechanism that is trapping it? And how can the water flowback data be used in estimating effective fracture volume using production data analysis tools? A number of simulation cases were run for single and two phase (gas/water) for modeling flowback and long-term production periods. Various physical assumptions were investigated for the saturations and properties that exist in the fracture/matrix system after hydraulic fracturing. The results of these simulations were compared with analytical solutions and data from actual wells using diagnostic and specialized plots. The results of these comparisons led to certain conclusions and procedures describing possible reservoir conditions after hydraulic fracturing and during production. Past publications have suggested that the lost frac water is trapped in the natural fracture or imbibed into the rock matrix near the fracture face. Natural fracture spacing could be a possible explanation of the lost frac water. These concepts are tested and the challenge of simulating a natural fracture with trapped water without imbibition is solved using a new hybrid relative permeability jail. This concept was tested for the period of flowback, shut-in and production. This work presents the benefits of a new method for combining water flowback and long-term water production data in shale gas analysis. Water production analysis can provide effective fracture volume which was confirmed by the cumulative produced water. This will help when evaluating fracture-stimulation jobs. It also shows the benefits of combining flowback and long-term water production data in the analysis of shale gas wells. In some cases, the time shift on diagnostic plots changes the apparent flow regime identification of early gas production data. This leads to different models of the fracture/matrix system. The presented work shows the importance of collecting and including water flowback data in long-term production data. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152548
Book Synopsis Gas Flow Through Shale by : Ahmad Sakhaee-Pour
Download or read book Gas Flow Through Shale written by Ahmad Sakhaee-Pour and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The growing demand for energy provides an incentive to pursue unconventional resources. Among these resources, tight gas and shale gas reservoirs have gained significant momentum because recent advances in technology allowed us to produce them at an economical rate. More importantly, they seem likely to contain a significant volume of hydrocarbon. There are, however, many questions concerning hydrocarbon production from these unconventional resources. For instance, in tight gas sandstone, we observe a significant variability in the producibilities of wells in the same field. The heterogeneity is even present in a single well with changes in depth. It is not clear what controls this heterogeneity. In shale gas, the pore connectivity inside the void space is not well explored and hence, a representative pore model is not available. Further, the effects of an adsorbed layer of gas and gas slippage on shale permeability are poorly understood. These effects play a crucial role in assigning a realistic permeability for shale in-situ from a laboratory measurement. In the laboratory, in contrast to in-situ, the core sample lacks the adsorbed layer because the permeability measurements are typically conducted at small pore pressures. Moreover, the gas slippages in laboratory and in-situ conditions are not identical. The present study seeks to investigate these discrepancies. Drainage and imbibition are sensitive to pore connectivity and unconventional gas transport is strongly affected by the connectivity. Hence, there is a strong interest in modeling mercury intrusion capillary pressure (MICP) test because it provides valuable information regarding the pore connectivity. In tight gas sandstone, the main objective of this research is to find a relationship between the estimated ultimate recovery (EUR) and the petrophysical properties measured by drainage/imbibition tests (mercury intrusion, withdrawal, and porous plate) and by resistivity analyses. As a measure of gas likely to be trapped in the matrix during production---and hence a proxy for EUR---we use the ratio of residual mercury saturation after mercury withdrawal (S[subscript gr]) to initial mercury saturation (S[subscript gi]), which is the saturation at the start of withdrawal. Crucially, a multiscale pore-level model is required to explain mercury intrusion capillary pressure measurements in these rocks. The multiscale model comprises a conventional network model and a tree-like pore structure (an acyclic network) that mimic the intergranular (macroporosity) and intragranular (microporosity) void spaces, respectively. Applying the multiscale model to porous plate data, we classify the pore spaces of rocks into macro-dominant, intermediate, and micro-dominant. These classes have progressively less drainage/imbibition hysteresis, which leads to the prediction that significantly more hydrocarbon is recoverable from microporosity than macroporosity. Available field data (production logs) corroborate the higher producibility of the microporosity. The recovery of hydrocarbon from micro-dominant pore structure is superior despite its inferior initial production (IP). Thus, a reservoir or a region in which the fraction of microporosity varies spatially may show only a weak correlation between IP and EUR. In shale gas, we analyze the pore structure of the matrix using mercury intrusion data to provide a more realistic model of pore connectivity. In the present study, we propose two pore models: dead-end pores and Nooks and Crannies. In the first model, the void space consists of many dead-end pores with circular pore throats. The second model supposes that the void space contains pore throats with large aspect ratios that are connected through the rock. We analyze both the scanning electron microscope (SEM) images of the shale and the effect of confining stress on the pore size distribution obtained from the mercury intrusion test to decide which pore model is representative of the in-situ condition. We conclude that the dead-end pores model is more representative. In addition, we study the effects of adsorbed layers of CH4 and of gas slippage in pore walls on the flow behavior in individual conduits of simple geometry and in networks of such conduits. The network is based on the SEM image and drainage experiment in shale. To represent the effect of adsorbed gas, the effective size of each throat in the network depends on the pressure. The hydraulic conductance of each throat is determined based on the Knudsen number (Kn) criterion. The results indicate that laboratory measurements made with N2 at ambient temperature and 5-MPa pressure, which is typical for the transient pulse decay method, overestimate the gas permeability in the early life of production by a factor of 4. This ratio increases if the measurement is run at ambient conditions because the low pressure enhances the slippage and reduces the thickness of the adsorbed layer. Moreover, the permeability increases nonlinearly as the in-situ pressure decreases during production. This effect contributes to mitigating the decline in production rates of shale gas wells. Laboratory data available in the literature for methane permeability at pressures below 7 MPa agree with model predictions of the effect of pressure.
Book Synopsis A Framework for the Prediction of Long-term Time-dependent Deformation of Shale by : Qing Yin
Download or read book A Framework for the Prediction of Long-term Time-dependent Deformation of Shale written by Qing Yin and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The long-term creep behavior of shale has become a major concern in different engineering applications, which reduces oil and gas production of shale reservoirs and triggers devastating landslides. While indentation creep tests at the nanoscale can reveal creep responses of single-material phases within minutes, long-term experimental studies on the bulk shale samples that last months to years are still limited by their time-consuming nature. Meanwhile, numerical studies on this subject are restricted to empirical formulations, creating little connection to the microstructures of the material. In this work, a framework for predicting the long-term creep behavior of shale is proposed based on a novel constitutive formulation, which bridges the creep response of the bulk shale sample at the centimeter scale and the mechanical properties of single-material phases at the sub-micron scale. The constitutive law developed in this work incorporates three material properties: heterogeneity, anisotropy, and viscoplasticity. Based on experimental results, the constitutive law considers a simplified two-material mixture of a softer phase representing clay and organics, and a harder phase representing inorganic matter. This setting captures two levels of heterogeneity: (1) the two-material mixture at one point representing the volume-average of the sub-micron scale heterogeneity, and (2) the variation of volume fractions from point to point representing the mesoscale heterogeneity in a centimeter-scale bulk shale sample. At the same time, it naturally bridges the mechanical responses from nanoscale to centimeter scale. Under the framework of the modified Cam-Clay critical state model, transverse isotropy is incorporated into the harder material and assumed for both elastic and viscoplastic responses. Time-dependent behavior is addressed by the viscoplastic formulations of Duvaut-Lions and Perzyna, which exhibit excellent convergence properties. To demonstrate the features of the constitutive formulations, a finite element package called GeoScale is developed and applied to several numerical examples. A triaxial creep test on the organic-rich Barnett shale is first simulated. While transverse isotropy is only incorporated in the harder material phase, the solution successfully captures the anisotropic creep responses along different directions of the bulk material, which shows a strong agreement with the experimental results. It is worth noting that similar results cannot be replicated by a one-material model with or without anisotropy, which further justifies the necessity of the two-material model. Second, strain localization in the form of dilative shear band is observed in a set of 2D plane strain simulations under a strain-driven approach, in which the different shear band patterns, either conjugate or single-dominating, are shown to result from various strain rates. In this example, it is worth noting that no element enhancement is needed to accommodate the localized deformation, as viscoplasticity in the formulation acts as a form of regularization. Furthermore, a shale sample with spatially varying volume fractions of material phases is loaded under a constant axial stress. It is shown that the proposed model can trigger multiple creep-induced shear bands, which develop along the weaker direction of the sample and grow in width. GeoScale is further extended to simulate indentation tests on Woodford shale at the nanometer and micrometer scales using an incremental frictionless multi-body contact algorithm based on the Lagrange multipliers method, along with our constitutive framework. Simulation results suggest that creep of the sample is mostly attributed to the viscoplastic deformation of the material away from the indenter tip, and that such response is highly dependent on the stress rate during the loading stage. The time-related material properties are calibrated from the nano- and micro-indentation experiments. As the calibrated material properties become available, the long-term creep behavior of shale is predicted by simulating 3D triaxial creep tests, marking the completion of this work.
Book Synopsis An Experimental Investigation of Pressure-dependent and Time-dependent Fracture Aperture and Permeability in Barnett Shale by : Yin Gong
Download or read book An Experimental Investigation of Pressure-dependent and Time-dependent Fracture Aperture and Permeability in Barnett Shale written by Yin Gong and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
