The Experts below are selected from a list of 8946 Experts worldwide ranked by ideXlab platform
Cy Kwok - One of the best experts on this subject based on the ideXlab platform.
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evolution of stress induced borehole breakout in inherently anisotropic Rock insights from discrete element modeling
Journal of Geophysical Research, 2016Co-Authors: Kang Duan, Cy KwokAbstract:The aim of this study is to better understand the mechanisms controlling the initiation, propagation, and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings. A two-dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic Rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs. Both isotropic and anisotropic hollow square-shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale. The isotropic model is validated by comparing the stress distribution around borehole wall and along X axis direction with analytical solutions. Effects of different factors including the particle size distribution, borehole diameter, far-field stress Anisotropy, and Rock Anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation. Simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks. Reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure. Rock Anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress. Far-field stress Anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings. Results from this study can provide fundamental insights on the underlying particle-scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic Rock.
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Evolution of stress-induced borehole breakout in inherently anisotropic Rock: Insights from discrete element modeling
'Wiley', 2016Co-Authors: Duan K, Cy KwokAbstract:The aim of this study is to better understand the mechanisms controlling the initiation, propagation, and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings. A two-dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic Rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs. Both isotropic and anisotropic hollow square-shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale. The isotropic model is validated by comparing the stress distribution around borehole wall and along X axis direction with analytical solutions. Effects of different factors including the particle size distribution, borehole diameter, far-field stress Anisotropy, and Rock Anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation. Simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks. Reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure. Rock Anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress. Far-field stress Anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings. Results from this study can provide fundamental insights on the underlying particle-scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic Rock.published_or_final_versio
Kang Duan - One of the best experts on this subject based on the ideXlab platform.
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evolution of stress induced borehole breakout in inherently anisotropic Rock insights from discrete element modeling
Journal of Geophysical Research, 2016Co-Authors: Kang Duan, Cy KwokAbstract:The aim of this study is to better understand the mechanisms controlling the initiation, propagation, and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings. A two-dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic Rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs. Both isotropic and anisotropic hollow square-shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale. The isotropic model is validated by comparing the stress distribution around borehole wall and along X axis direction with analytical solutions. Effects of different factors including the particle size distribution, borehole diameter, far-field stress Anisotropy, and Rock Anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation. Simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks. Reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure. Rock Anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress. Far-field stress Anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings. Results from this study can provide fundamental insights on the underlying particle-scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic Rock.
Baotang Shen - One of the best experts on this subject based on the ideXlab platform.
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modelling fracture propagation in anisotropic Rock mass
Rock Mechanics and Rock Engineering, 2015Co-Authors: Baotang Shen, Topias Siren, Mikael RinneAbstract:Anisotropic Rock mass is often encountered in Rock engineering, and cannot be simplified as an isotropic problem in numerical models. A good understanding of Rock fracturing processes and the ability to predict fracture initiation and propagation in anisotropic Rock masses are required for many Rock engineering problems. This paper describes the development of the anisotropic function in FRACOD—a specialized fracture propagation modelling software—and its recent applications to Rock engineering issues. Rock Anisotropy includes strength Anisotropy and modulus Anisotropy. The level of complexity in developing the anisotropic function for strength Anisotropy and modulus Anisotropy in FRACOD is significantly different. The strength Anisotropy function alone does not require any alteration in the way that FRACOD calculates Rock stress and displacement, and therefore is relatively straightforward. The modulus Anisotropy function, on the other hand, requires modification of the fundamental equations of stress and displacement in FRACOD, a boundary element code, and hence is more complex and difficult. In actual Rock engineering, the strength Anisotropy is often considered to be more pronounced and important than the modulus Anisotropy, and dominates the stability and failure pattern of the Rock mass. The modulus Anisotropy will not be considered in this study. This paper discusses work related to the development of the strength Anisotropy in FRACOD. The Anisotropy function has been tested using numerical examples. The predicted failure surfaces are mostly along the weakest planes. Predictive modelling of the Posiva’s Olkiluoto Spalling Experiment was made. The model suggests that spalling is very sensitive to the direction of Anisotropy. Recent observations from the in situ experiment showed that shear fractures rather than tensile fractures occur in the holes. According to the simulation, the maximum tensile stress is well below the tensile strength, but the maximum shear stress is probably enough to displace mica contact.
Mikael Rinne - One of the best experts on this subject based on the ideXlab platform.
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modelling fracture propagation in anisotropic Rock mass
Rock Mechanics and Rock Engineering, 2015Co-Authors: Baotang Shen, Topias Siren, Mikael RinneAbstract:Anisotropic Rock mass is often encountered in Rock engineering, and cannot be simplified as an isotropic problem in numerical models. A good understanding of Rock fracturing processes and the ability to predict fracture initiation and propagation in anisotropic Rock masses are required for many Rock engineering problems. This paper describes the development of the anisotropic function in FRACOD—a specialized fracture propagation modelling software—and its recent applications to Rock engineering issues. Rock Anisotropy includes strength Anisotropy and modulus Anisotropy. The level of complexity in developing the anisotropic function for strength Anisotropy and modulus Anisotropy in FRACOD is significantly different. The strength Anisotropy function alone does not require any alteration in the way that FRACOD calculates Rock stress and displacement, and therefore is relatively straightforward. The modulus Anisotropy function, on the other hand, requires modification of the fundamental equations of stress and displacement in FRACOD, a boundary element code, and hence is more complex and difficult. In actual Rock engineering, the strength Anisotropy is often considered to be more pronounced and important than the modulus Anisotropy, and dominates the stability and failure pattern of the Rock mass. The modulus Anisotropy will not be considered in this study. This paper discusses work related to the development of the strength Anisotropy in FRACOD. The Anisotropy function has been tested using numerical examples. The predicted failure surfaces are mostly along the weakest planes. Predictive modelling of the Posiva’s Olkiluoto Spalling Experiment was made. The model suggests that spalling is very sensitive to the direction of Anisotropy. Recent observations from the in situ experiment showed that shear fractures rather than tensile fractures occur in the holes. According to the simulation, the maximum tensile stress is well below the tensile strength, but the maximum shear stress is probably enough to displace mica contact.
J. Zhao - One of the best experts on this subject based on the ideXlab platform.
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a microstructure based model to characterize micromechanical parameters controlling compressive and tensile failure in crystallized Rock
Rock Mechanics and Rock Engineering, 2014Co-Authors: T. Kazerani, J. ZhaoAbstract:A discrete element model is proposed to examine Rock strength and failure. The model is implemented by UDEC which is developed for this purpose. The material is represented as a collection of irregular-sized deformable particles interacting at their cohesive boundaries. The interface between two adjacent particles is viewed as a flexible contact whose stress–displacement law is assumed to control the material fracture and fragmentation process. To reproduce Rock Anisotropy, an innovative orthotropic cohesive law is developed for contact which allows the interfacial shear and tensile behaviours to be different from each other. The model is applied to a crystallized igneous Rock and the individual and interactional effects of the microstructural parameters on the material compressive and tensile failure response are examined. A new methodical calibration process is also established. It is shown that the model successfully reproduces the Rock mechanical behaviour quantitatively and qualitatively. Ultimately, the model is used to understand how and under what circumstances micro-tensile and micro-shear cracking mechanisms control the material failure at different loading paths.
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A Discrete Element Model for Predicting Shear Strength and Degradation of Rock Joint by Using Compressive and Tensile Test Data
Rock Mechanics and Rock Engineering, 2012Co-Authors: T. Kazerani, Z. Y. Yang, J. ZhaoAbstract:A discrete element model is proposed to examine Rock strength and failure. The model is implemented by UDEC, which is developed for this purpose. The material is represented as a collection of irregular-sized deformable particles interacting at their cohesive boundaries. The interface between two adjacent particles is viewed as a flexible contact whose constitutive law controls the material fracture and fragmentation properties. To reproduce Rock Anisotropy, an orthotropic cohesive law is developed for the contacts, which allows their shear and tensile behaviors to be different from each other. Using a combination of original closed-form expressions and statistical calibrations, a unique set of the contact microparameters are found based on the uniaxial/triaxial compression and Brazilian tension test data of a plaster. Applying the obtained microparameters, joint specimens, made of the same plaster, are simulated, where the comparison of the obtained results to laboratory data shows a reasonable agreement.
