ABSTRACT: The Stability Graph is an accepted tool for open stope design in the metalliferous underground mining community. Since its development in 1981, it has undergone several modifications and remains active research subject to date. Admittedly, while some of the suggested changes have been called into question for their practical relevance, others have gone a long way to improve the reliability of the method in minimizing dilution in open stope mining. One of the major concerns that have emerged in researching some suggested modifications to the design tool appears to be those authors behind such propositions neither understand how the method works nor the database used to develop the method. Such authors rely on the application of statistics to the database with no idea of the practical implications of the outcome of their analysis except that it is probably statistically beautiful in theory. The downside of this playing with numbers is that so much confusion has been created in the mining industry as to what is useful in using the method for open stope design. This paper cautions against the misuse of statistics in geoengineering with emphasis on the Stability Graph and provides recent developments relevant to improving the reliability of the method in reducing dilution in open stopes. Furthermore, the long outstanding question of whether the original Stability Graph number factors or the modified Stability Graph number factors should be used or not is answered.
{"title":"The Qualitative Stability Graph for Open Stope Design – Recent Developments","authors":"Fidelis T. Suorineni, Y. Madenova","doi":"10.56952/arma-2022-0017","DOIUrl":"https://doi.org/10.56952/arma-2022-0017","url":null,"abstract":"ABSTRACT: The Stability Graph is an accepted tool for open stope design in the metalliferous underground mining community. Since its development in 1981, it has undergone several modifications and remains active research subject to date. Admittedly, while some of the suggested changes have been called into question for their practical relevance, others have gone a long way to improve the reliability of the method in minimizing dilution in open stope mining. One of the major concerns that have emerged in researching some suggested modifications to the design tool appears to be those authors behind such propositions neither understand how the method works nor the database used to develop the method. Such authors rely on the application of statistics to the database with no idea of the practical implications of the outcome of their analysis except that it is probably statistically beautiful in theory. The downside of this playing with numbers is that so much confusion has been created in the mining industry as to what is useful in using the method for open stope design. This paper cautions against the misuse of statistics in geoengineering with emphasis on the Stability Graph and provides recent developments relevant to improving the reliability of the method in reducing dilution in open stopes. Furthermore, the long outstanding question of whether the original Stability Graph number factors or the modified Stability Graph number factors should be used or not is answered.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124918754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Lindenbach, Steve Dalton, R. Bearce, Gergo Arany
Rock mass modulus, also referred to as the deformation modulus, is an important input variable for any load-deformation analysis of a foundation, such as a finite-element analysis for a dam. As the representative volume of rock is increased the rock mass will appear weaker and more deformable due to the inclusion of more discontinuities. The rock mass modulus can be measured directly downhole with a variety of devices, such as a uniaxial or radial jacking rig, a flat jack, or more commonly, a dilatometer. Modulus values can be estimated indirectly using site-specific empirical relationships.This paper provides a comparison of field- and laboratory-derived rock mass modulus values in an effort to develop a range of likely parameters and evaluate data quality/confidence levels. The in-situ values were compared to values developed from eight commonly used empirical relationships. Results indicate that the dilatometer-measured and empirically estimated values are similar where the rock is massive and relatively intact but vary significantly where the rock is fractured or weathered. These significant variations appear to be related to how the rock deforms in unconfined/semi-confined conditions (i.e., failure occurs into open space).
{"title":"A Comparison Between Field-Measured and Empirically Estimated Rock Mass Modulus Values","authors":"E. Lindenbach, Steve Dalton, R. Bearce, Gergo Arany","doi":"10.56952/arma-2022-0130","DOIUrl":"https://doi.org/10.56952/arma-2022-0130","url":null,"abstract":"Rock mass modulus, also referred to as the deformation modulus, is an important input variable for any load-deformation analysis of a foundation, such as a finite-element analysis for a dam. As the representative volume of rock is increased the rock mass will appear weaker and more deformable due to the inclusion of more discontinuities. The rock mass modulus can be measured directly downhole with a variety of devices, such as a uniaxial or radial jacking rig, a flat jack, or more commonly, a dilatometer. Modulus values can be estimated indirectly using site-specific empirical relationships.This paper provides a comparison of field- and laboratory-derived rock mass modulus values in an effort to develop a range of likely parameters and evaluate data quality/confidence levels. The in-situ values were compared to values developed from eight commonly used empirical relationships. Results indicate that the dilatometer-measured and empirically estimated values are similar where the rock is massive and relatively intact but vary significantly where the rock is fractured or weathered. These significant variations appear to be related to how the rock deforms in unconfined/semi-confined conditions (i.e., failure occurs into open space).","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124980802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Geomechanical rock properties have a broad impact on drilling, completion, production, and reservoir management decisions. Accurate quantification of measurements and correctly propagating uncertainty throughout the modeling process can improve decision quality and reduce the cost of field development. Laboratory rock property tests are generally sparse. To build a mechanical earth model for the entire field, empirical correlations are used to bridge the gap between lab data and petrophysical or geophysical measurements. Empirical correlations often rely on limited core test data from one or a few fields for a specific formation. This makes applying a correlation that is developed for a specific field to other fields difficult.A Bayesian machine learning approach is presented for modeling the rock properties. It provides a robust framework for building multivariate rock property models and evaluating uncertainties associated with the model. Core test data from many different fields with large variations of properties were used for this study. The workflow uses a hierarchical Bayesian regression, which enables the accurate learning of field-specific correlations in fields with much data and borrowing of correlation information from other fields in fields with little data.
{"title":"Geomechanics Rock Property Uncertainty Workflow using a Bayesian Machine Learning Framework","authors":"P. Ray, Shuxing Cheng, Arthur Lui, Devin Francom","doi":"10.56952/arma-2022-0104","DOIUrl":"https://doi.org/10.56952/arma-2022-0104","url":null,"abstract":"Geomechanical rock properties have a broad impact on drilling, completion, production, and reservoir management decisions. Accurate quantification of measurements and correctly propagating uncertainty throughout the modeling process can improve decision quality and reduce the cost of field development. Laboratory rock property tests are generally sparse. To build a mechanical earth model for the entire field, empirical correlations are used to bridge the gap between lab data and petrophysical or geophysical measurements. Empirical correlations often rely on limited core test data from one or a few fields for a specific formation. This makes applying a correlation that is developed for a specific field to other fields difficult.A Bayesian machine learning approach is presented for modeling the rock properties. It provides a robust framework for building multivariate rock property models and evaluating uncertainties associated with the model. Core test data from many different fields with large variations of properties were used for this study. The workflow uses a hierarchical Bayesian regression, which enables the accurate learning of field-specific correlations in fields with much data and borrowing of correlation information from other fields in fields with little data.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126062491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hanqing Wang, H. Pang, Yan Jin, Yunhu Lu, Yongdong Fan
Mud loss is one of the most common and troublesome wellbore problems. Predictive evaluation of mud loss types not only optimizes drilling design, but also reduces potential costs before drilling. To solve mud loss problem of M formation in the H oil field, we proposed a practical solution based on machine learning in this paper, which can predict the mud loss types using seismic data. Firstly, we calculated and obtained 16 seismic attributes in 6 categories, and according to the mud loss rate and volume, we classified the mud loss into four types: seepage loss, partial loss, severe loss, and total loss. Then 10 characteristics wells were selected from 50 wells, which covered different mud loss types and depth. The seismic attributes of single well with the above characteristics were extracted, and the relationship between seismic attributes and mud loss type were obtained using machine learning. Finally, a 3D probability prediction model of potential mud loss type is obtained and analyzed with a practical case. Our model can predict the distribution of mud loss types at different depths in different regions. It can not only be used in the design of well location and well trajectory but also provide scientific suggestions for mud loss prevention and plugging.
{"title":"Prediction of mud loss type based on seismic data using machine learning","authors":"Hanqing Wang, H. Pang, Yan Jin, Yunhu Lu, Yongdong Fan","doi":"10.56952/arma-2022-0485","DOIUrl":"https://doi.org/10.56952/arma-2022-0485","url":null,"abstract":"Mud loss is one of the most common and troublesome wellbore problems. Predictive evaluation of mud loss types not only optimizes drilling design, but also reduces potential costs before drilling. To solve mud loss problem of M formation in the H oil field, we proposed a practical solution based on machine learning in this paper, which can predict the mud loss types using seismic data. Firstly, we calculated and obtained 16 seismic attributes in 6 categories, and according to the mud loss rate and volume, we classified the mud loss into four types: seepage loss, partial loss, severe loss, and total loss. Then 10 characteristics wells were selected from 50 wells, which covered different mud loss types and depth. The seismic attributes of single well with the above characteristics were extracted, and the relationship between seismic attributes and mud loss type were obtained using machine learning. Finally, a 3D probability prediction model of potential mud loss type is obtained and analyzed with a practical case. Our model can predict the distribution of mud loss types at different depths in different regions. It can not only be used in the design of well location and well trajectory but also provide scientific suggestions for mud loss prevention and plugging.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123739910","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bedding plane properties influence the failure behavior of laminated rocks such as slate and shale. For safe and stable underground coal mine design it is imperative to understand the relationship between the bedding plane strength and the failure of laminated rock. However, it is difficult to obtain in situ laminated rocks with various bedding plane properties while keeping other properties constant. In the present research, we experimentally investigated various approaches to vary the weak plane cohesive strength (Cp). Concrete block incorporating a weak plane was casted and the Cp of the weak plane was varied experimentally using two methods. Direct shear tests along the planes validated that applying normal stress on the concrete block successfully varied the Cp. The verified method was then used to cast synthetic laminated rock (SLR) with various Cp. We then conducted Brazilian splitting tests on SLR with different orientations of bedding planes and compared the failure strength and failure modes with that of shale specimen. The results validated the second method as both failure strength and failure modes of SLR specimens matched the behavior of shale specimens. This research provided a validated method to fabricate SLR with different Cp in the laboratory.
{"title":"Experimental Investigation to Fabricate Synthetic Laminated Rock with Different Bedding Plane Cohesive Strengths","authors":"Qingwen Shi, Brijes Mishra","doi":"10.56952/arma-2022-0747","DOIUrl":"https://doi.org/10.56952/arma-2022-0747","url":null,"abstract":"Bedding plane properties influence the failure behavior of laminated rocks such as slate and shale. For safe and stable underground coal mine design it is imperative to understand the relationship between the bedding plane strength and the failure of laminated rock. However, it is difficult to obtain in situ laminated rocks with various bedding plane properties while keeping other properties constant. In the present research, we experimentally investigated various approaches to vary the weak plane cohesive strength (Cp). Concrete block incorporating a weak plane was casted and the Cp of the weak plane was varied experimentally using two methods. Direct shear tests along the planes validated that applying normal stress on the concrete block successfully varied the Cp. The verified method was then used to cast synthetic laminated rock (SLR) with various Cp. We then conducted Brazilian splitting tests on SLR with different orientations of bedding planes and compared the failure strength and failure modes with that of shale specimen. The results validated the second method as both failure strength and failure modes of SLR specimens matched the behavior of shale specimens. This research provided a validated method to fabricate SLR with different Cp in the laboratory.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125487986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. M. Mueller, G. Couples, P. Sahay, Jonás D. De Basabe
Continuum poroelasticity theories provide a macroscopic description of fluid-saturated porous media so that pore-scale features only emerge in some averaged form.However, therein the specific signature of the underpinning micro-structure is not transparent in the constitutive material equations.For a regular lattice-type micromechanical model, we derive an exact formula for the Biot coefficient.As anticipated by experimental and numerical studies, the Biot coefficient embodies a nonlinear combination of the elasticity of the solid phase material and the geometry characterizing the pore space.This result allows us to exemplify the abstract concept of pore boundary deformation appearing in the continuum description of porous media including the ramifications of a geometrical self-similar deformation.Although this is certainly an oversimplified model for most porous rocks, our analysis may serve as benchmark for numerical upscaling based on digitized images to infer the poroelastic material parameters and thus to support ongoing experimental efforts to measure poroelasticity coefficients.
{"title":"Pore boundary deformation and the Biot coefficient: a micromechanical analysis","authors":"T. M. Mueller, G. Couples, P. Sahay, Jonás D. De Basabe","doi":"10.56952/arma-2022-0692","DOIUrl":"https://doi.org/10.56952/arma-2022-0692","url":null,"abstract":"Continuum poroelasticity theories provide a macroscopic description of fluid-saturated porous media so that pore-scale features only emerge in some averaged form.However, therein the specific signature of the underpinning micro-structure is not transparent in the constitutive material equations.For a regular lattice-type micromechanical model, we derive an exact formula for the Biot coefficient.As anticipated by experimental and numerical studies, the Biot coefficient embodies a nonlinear combination of the elasticity of the solid phase material and the geometry characterizing the pore space.This result allows us to exemplify the abstract concept of pore boundary deformation appearing in the continuum description of porous media including the ramifications of a geometrical self-similar deformation.Although this is certainly an oversimplified model for most porous rocks, our analysis may serve as benchmark for numerical upscaling based on digitized images to infer the poroelastic material parameters and thus to support ongoing experimental efforts to measure poroelasticity coefficients.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115046907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Birchwood, Evangelia Nicolaidou, A. Rodriguez-herrera, R. Prioul
Wellbore stability models are used in well-planning to determine the safe mud-weight window for drilling. More generally, calibration of wellbore stability models against observations (such as image logs, caliper measurements, and generaldrilling observations) is an essential step in constructing reliable 1D and 3D Mechanical Earth Models (MEMs) which are used to design safe drilling, completion, and production strategies. However, such calibration usually produces non-unique results, partly because most common types of calibration data impose only soft (inequality) constraints on wellbore stability models. Such nonuniqueness can be represented using probability density functions (PDFs). In this paper we show the results of stochastic inversion for stress parameters performed by drawing samples from these PDFs using a Markov Chain Monte Carlo procedure. Most types of calibration data (e.g., breakouts, drilling-induced fractures) produce a wide range of possible solutions for the stress parameters. However, the uncertainty reduces dramatically as data from an increasing number of depth locations is simultaneously inverted. The results also illustrate how including depths where breakouts and drilling-induced fractures are absent produces a powerful constraint on inferred stress parameters.
{"title":"Stochastic Inversion of Wellbore Stability Models Calibrated With Hard and Soft Data","authors":"R. Birchwood, Evangelia Nicolaidou, A. Rodriguez-herrera, R. Prioul","doi":"10.56952/arma-2022-0774","DOIUrl":"https://doi.org/10.56952/arma-2022-0774","url":null,"abstract":"Wellbore stability models are used in well-planning to determine the safe mud-weight window for drilling. More generally, calibration of wellbore stability models against observations (such as image logs, caliper measurements, and generaldrilling observations) is an essential step in constructing reliable 1D and 3D Mechanical Earth Models (MEMs) which are used to design safe drilling, completion, and production strategies. However, such calibration usually produces non-unique results, partly because most common types of calibration data impose only soft (inequality) constraints on wellbore stability models. Such nonuniqueness can be represented using probability density functions (PDFs). In this paper we show the results of stochastic inversion for stress parameters performed by drawing samples from these PDFs using a Markov Chain Monte Carlo procedure. Most types of calibration data (e.g., breakouts, drilling-induced fractures) produce a wide range of possible solutions for the stress parameters. However, the uncertainty reduces dramatically as data from an increasing number of depth locations is simultaneously inverted. The results also illustrate how including depths where breakouts and drilling-induced fractures are absent produces a powerful constraint on inferred stress parameters.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122794546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shiyuan Li, Hao Huang, Yiyang Pan, Jingya Zhao, L. Guo, Leyan Yang
Shale oil and gas resources are currently an important replacement resource for oil and gas in China and have huge potential development. During the mining process, the reservoir shale has creep characteristics due to its own physical properties and mineral composition, which causes the artificial fracturing network to produce a closure effect, which affects the production capacity of the reservoir. This work mainly studies the creep characteristics of reservoir shale and its influence on reservoir productivity. The shale in Chang-7 block of Yanchang formation in the Ordos Basin is selected as the research object. The triaxial creep experiment is used to determine that the shale creep law conforms to the power order. The Abaqus finite element analysis software is used to simulate the creep of the shale sample under the creep time of 1 year, 5 years, and 10 years to observe the changes of reservoir fractures under the action, evaluate the degree of fracture closure, and analyze the effect of creep on reservoir conductivity. The research results show that shale reservoir creep will cause proppant embedment and fracture closure, non-linear reduction of reservoir conductivity, and the growth rate of production gradually slowed down by the effect of time.
{"title":"Numerical simulation study on creep characteristics and fracture closure of deep shale","authors":"Shiyuan Li, Hao Huang, Yiyang Pan, Jingya Zhao, L. Guo, Leyan Yang","doi":"10.56952/arma-2022-2073","DOIUrl":"https://doi.org/10.56952/arma-2022-2073","url":null,"abstract":"Shale oil and gas resources are currently an important replacement resource for oil and gas in China and have huge potential development. During the mining process, the reservoir shale has creep characteristics due to its own physical properties and mineral composition, which causes the artificial fracturing network to produce a closure effect, which affects the production capacity of the reservoir. This work mainly studies the creep characteristics of reservoir shale and its influence on reservoir productivity. The shale in Chang-7 block of Yanchang formation in the Ordos Basin is selected as the research object. The triaxial creep experiment is used to determine that the shale creep law conforms to the power order. The Abaqus finite element analysis software is used to simulate the creep of the shale sample under the creep time of 1 year, 5 years, and 10 years to observe the changes of reservoir fractures under the action, evaluate the degree of fracture closure, and analyze the effect of creep on reservoir conductivity. The research results show that shale reservoir creep will cause proppant embedment and fracture closure, non-linear reduction of reservoir conductivity, and the growth rate of production gradually slowed down by the effect of time.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114396365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Geomaterials are porous, and there are air, water and other liquids inside the pore space. Pore pressure fluctuation may result in the change of contact forces between the solid grains. The deformation of solid skeleton changes the size of pore and therefore the fluid flows inside the pore space. The coupled process is often described with the mixture theory in continuum mechanics. Localized deformation may lead to the displacement discontinuity or the fracture, increasing the complexity of the whole fluid-solid coupled process. Numerical simulations of the complex processes in the subsurface are essential in understanding many geoengineering systems, such as hydraulic fracturing, geological fault reactivation, waste water management, geothermal energy extraction and CO2 sequestration and so on. This paper presents an assumed enhanced strain (AES) finite element method to model the fracture evolution in porous media, where the discontinuous function enrichments are introduced into the displacement approximation to simulate fracture deformation. The enriched degrees of freedom can be removed by the standard static condensation method, which means the method does not introduce additional global system of equations. The mass and stress coupling is described by the standard Biot's poro-elasticity theory. The numerical method is verified by the mesh sensitivity studies and comparisons with analytical solutions. Particularly, with the AES framework, we have numerically compared the cohesive fracture model and linear elastic fracture mechanics model for simulating hydraulic fracture propagation in porous media.
{"title":"A numerical comparison of linear elastic and cohesive fracture models for hydraulic fracturing based on assumed enhanced strain (AES) method","authors":"Fushen Liu","doi":"10.56952/arma-2022-0416","DOIUrl":"https://doi.org/10.56952/arma-2022-0416","url":null,"abstract":"Geomaterials are porous, and there are air, water and other liquids inside the pore space. Pore pressure fluctuation may result in the change of contact forces between the solid grains. The deformation of solid skeleton changes the size of pore and therefore the fluid flows inside the pore space. The coupled process is often described with the mixture theory in continuum mechanics. Localized deformation may lead to the displacement discontinuity or the fracture, increasing the complexity of the whole fluid-solid coupled process. Numerical simulations of the complex processes in the subsurface are essential in understanding many geoengineering systems, such as hydraulic fracturing, geological fault reactivation, waste water management, geothermal energy extraction and CO2 sequestration and so on. This paper presents an assumed enhanced strain (AES) finite element method to model the fracture evolution in porous media, where the discontinuous function enrichments are introduced into the displacement approximation to simulate fracture deformation. The enriched degrees of freedom can be removed by the standard static condensation method, which means the method does not introduce additional global system of equations. The mass and stress coupling is described by the standard Biot's poro-elasticity theory. The numerical method is verified by the mesh sensitivity studies and comparisons with analytical solutions. Particularly, with the AES framework, we have numerically compared the cohesive fracture model and linear elastic fracture mechanics model for simulating hydraulic fracture propagation in porous media.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122203788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. L. Malki, V. Rasouli, M. Saberi, I. Mellal, O. Ozotta, B. Sennaoui, Hichem A. K. Chellal
The velocity-porosity relationship depends on many factors such as grain shape, sorting, chemical composition, and diagenesis processes. Fluids always occupy the pore space and pore shape plays a significant role in rock stiffness. The Bakken Petroleum System (BPS) in the Williston Basin, North Dakota, consists of the Bakken formation and three folks reservoirs. Bakken formation is divided into three members: Upper Bakken (UB), Lower Bakken (LB), and Middle Bakken (MB), while Three Forks (TF) formation divided into five different units. Although clastic formation’s pores spaces are homogeneous, carbonates present pores heterogeneity which makes their elastic properties estimation complex. This heterogeneity is represented by different pore shapes captured from thin sections, where the aspect ratio (a) defines multiple pore types such as cracks, intergranular, and moldic pores. Furthermore, the pore filling material is a mixture of gas, oil, water, and kerogen in organic-rich shale. This study aims to analyze the effect of mineral composition, pore shape, and fluid type on rock properties of the BPS using various rock physics models. Our results showed that both compressional and shear velocities decreased for all fluid types. We also observed that filling pores with different fluids affect the elastic properties differently, based on their pore geometry, porosity, and lithology.
{"title":"Effect of Mineralogy, Pore Geometry, and Fluid Type on the Elastic Properties of the Bakken Formation","authors":"M. L. Malki, V. Rasouli, M. Saberi, I. Mellal, O. Ozotta, B. Sennaoui, Hichem A. K. Chellal","doi":"10.56952/arma-2022-0147","DOIUrl":"https://doi.org/10.56952/arma-2022-0147","url":null,"abstract":"The velocity-porosity relationship depends on many factors such as grain shape, sorting, chemical composition, and diagenesis processes. Fluids always occupy the pore space and pore shape plays a significant role in rock stiffness. The Bakken Petroleum System (BPS) in the Williston Basin, North Dakota, consists of the Bakken formation and three folks reservoirs. Bakken formation is divided into three members: Upper Bakken (UB), Lower Bakken (LB), and Middle Bakken (MB), while Three Forks (TF) formation divided into five different units. Although clastic formation’s pores spaces are homogeneous, carbonates present pores heterogeneity which makes their elastic properties estimation complex. This heterogeneity is represented by different pore shapes captured from thin sections, where the aspect ratio (a) defines multiple pore types such as cracks, intergranular, and moldic pores. Furthermore, the pore filling material is a mixture of gas, oil, water, and kerogen in organic-rich shale. This study aims to analyze the effect of mineral composition, pore shape, and fluid type on rock properties of the BPS using various rock physics models. Our results showed that both compressional and shear velocities decreased for all fluid types. We also observed that filling pores with different fluids affect the elastic properties differently, based on their pore geometry, porosity, and lithology.","PeriodicalId":418045,"journal":{"name":"Proceedings 56th US Rock Mechanics / Geomechanics Symposium","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128514155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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