The effect of the fracture distribution on CO 2 injection into coal seams was studied with a heterogeneous model having dual porosity to represent both the primary medium (the coal matrix) and the secondary medium (th...The effect of the fracture distribution on CO 2 injection into coal seams was studied with a heterogeneous model having dual porosity to represent both the primary medium (the coal matrix) and the secondary medium (the fractures) under variable stress conditions. A numerical generation method and a digital image processing method were used to model the heterogeneous fracture distribution in the coal. The model solutions demonstrate that: (1) the fractures are the main channel for gas flow and their distribution has an important impact on the gas injection rate; (2) the fractures only affect the injection rate of CO 2 into the coal but not the final storage amount; (3) when gas is injected into coal the fractures will first expand and then close due to the changing effective stresses and the adsorption induced swelling of coal grains. This fully coupled dual-porosity model with a heterogeneous fracture distribution provides a way to predict the CO 2 injection into a coal seam.展开更多
Gently dipping fractures subjected to river incision are widely distributed on rock slopes.In this paper,a rock slope on the Nujiang River(China)is investigated to study the role of gently dipping fractures in the roc...Gently dipping fractures subjected to river incision are widely distributed on rock slopes.In this paper,a rock slope on the Nujiang River(China)is investigated to study the role of gently dipping fractures in the rock slopes evolution.Detailed field surveys indicate that gentle fractures are concentrated in four main zones.Moreover,the kinematics of the fracture system suggest that the genesis of these fractures can be synthesized into a progressive evolution model.This model indicates that the joints begin with the formation of an array of en echelon cracks that are subjected to continued crack elongation and shearing before ultimately approaching one another and interacting to form a complex joint system.Geomechanical analysis is performed to reveal the mechanisms of this genesis,and three main fracture patterns are identified based on the slope stress and are classified with respect to the slope evolution.Based on the detail field investigations and the evolutionary history of the river valley,we propose that intermittent incision by the river was the main factor contributing to the concentrated distribution of gently dipping joints.展开更多
The deep Lower Jurassic Ahe Formation(J_(1a))in the Dibei–Tuzi area of the Kuqa Depression has not been extensively explored because of the complex distribution of fractures.A study was conducted to investigate the r...The deep Lower Jurassic Ahe Formation(J_(1a))in the Dibei–Tuzi area of the Kuqa Depression has not been extensively explored because of the complex distribution of fractures.A study was conducted to investigate the relationship between the natural fracture distribution and structural style.The J_(1a)fractures in this area were mainly high-angle shear fractures.A backward thrust structure(BTS)is favorable for gas migration and accumulation,probably because natural fractures are more developed in the middle and upper parts of a thick competent layer.The opposing thrust structure(OTS)was strongly compressed,and the natural fractures in the middle and lower parts of the thick competent layer around the fault were more intense.The vertical fracture distribution in the thick competent layers of an imbricate-thrust structure(ITS)differs from that of BTS and OTS.The intensity of the fractures in the ITS anticline is similar to that in the BTS.Fracture density in monoclinic strata in a ITS is controlled by faulting.Overall,the structural style controls the configuration of faults and anticlines,and the stress on the competent layers,which significantly affects deep gas reservoir fractures.The enrichment of deep tight sandstone gas is likely controlled by two closely spaced faults and a fault-related anticline.展开更多
Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kin...Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr＇s circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; （stress induced critical martensite transformation temperature） would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.展开更多
Model I quasi-static nonlinear fracture of aluminum foams is analyzed by considering the effect of microscopic heterogeneity. Firstly, a continuum constitutive model is adopted to account for the plastic compressibili...Model I quasi-static nonlinear fracture of aluminum foams is analyzed by considering the effect of microscopic heterogeneity. Firstly, a continuum constitutive model is adopted to account for the plastic compressibility of the metallic foams. The yield strain modeled by a two- parameter Weibull-type function is adopted in the constitutive model. Then, a modified cohesive zone model is established to characterize the fracture behavior of aluminum foams with a cohesive zone ahead of the initial crack. The tensile traction versus local crack opening displacement relation is employed to describe the softening characteristics of the material. And a Weibull statistical model for peak bridging stress within the fracture process zone is used for considering microscopic heterogeneity of aluminum foams. Lastly, the influence of stochastic parameters on the curve of stress-strain is given. Numerical examples are given to illustrate the numerical model presented in this paper and the effects of Weibull parameters and material properties on J-integral are discussed.展开更多
Natural fractures(NFs)are common in shale and tight reservoirs,where staged multi-cluster fracturing of horizontal wells is a prevalent technique for reservoir stimulation.While NFs and stress interference are recogni...Natural fractures(NFs)are common in shale and tight reservoirs,where staged multi-cluster fracturing of horizontal wells is a prevalent technique for reservoir stimulation.While NFs and stress interference are recognized as significant factors affecting hydraulic fracture(HF)propagation,the combined influence of these factors remains poorly understood.To address this knowledge gap,a novel coupled hydromechanical-damage(HMD)model based on the phase field method is developed to investigate the propagation of multi-cluster HFs in fractured reservoirs.The comprehensive energy functional and control functions are established,while incorporating dynamic fluid distribution between multiple perforation clusters and refined changes in rock mechanical parameters during hydraulic fracturing.The HMD coupled multi-cluster HF propagation model investigates various scenarios,including single HF and single NF,reservoir heterogeneity,single HF and NF clusters,and multi-cluster HFs with NF clusters.The results show that the HMD coupling model can accurately capture the impact of approach angle(θ),stress difference and cementation strength on the interaction of HF and NF.The criterion of the open and cross zones is not fixed.The NF angle(a)is not a decisive parameter to discriminate the interaction.According to the relationship between approach angle(θ)and NF angle(a),the contact relationship of HF can be divided into three categories(θ=a,θ<a,andθ>a).The connected NF can increase the complexity of HF by inducing it to form branch fracture,resulting in a fractal dimension of HF as high as2.1280 at angles of±45°.Inter-fracture interference from the heel to the toe of HF shows the phenomenon of no,strong and weak interference.Interestingly,under the influence of NFs,distant HFs from the injection can become dominant fractures.However,as a gradually increases,inter-fracture stress interference becomes the primary factor influencing HF propagation,gradually superseding the dominance of NF induced fractures.展开更多
Groundwater inflow constitutes a critical challenge in rock tunnel engineering.This study systematically investigates the coupled effects of fracture spatial distribution and rock matrix permeability on tunnel water i...Groundwater inflow constitutes a critical challenge in rock tunnel engineering.This study systematically investigates the coupled effects of fracture spatial distribution and rock matrix permeability on tunnel water inflow using a novel embedded discrete fracture model based method.A set of quadratic regression models is established to delineate the relationship between inflow rate and fracture distribution parameters over a wide range of fracture-to-matrix permeability ratios(kf/km).Results demonstrate that fracture aperture,spacing,and their interaction dominate the inflow across all permeability ratios.Analysis of variance further reveals a threshold-dependent behavior:coupled effects are significant below a critical kf/km value but decay markedly above it.This threshold decreases with larger aperture and increases with wider spacing,yet remains nearly independent of fracture dip angle.Moreover,when kf/km is below the threshold,aperture and spacing exert greater influence on tunnel inflow at lower permeability ratios,while kf/km gains influence under larger apertures and smaller spacings.Finally,a case study of Nanwan Tunnel shows that matrix permeability plays a dual role—increasing the mean inflow rate while reducing uncertainty from stochastic fracture distribution.展开更多
To elucidate the adsorption characteristics and retention mechanisms of fracturing fluids in diverse clay minerals,we conducted on-line nuclear magnetic resonance(NMR)and atomic force microscopy(AFM)experiments.The de...To elucidate the adsorption characteristics and retention mechanisms of fracturing fluids in diverse clay minerals,we conducted on-line nuclear magnetic resonance(NMR)and atomic force microscopy(AFM)experiments.The depth and extent of solid phase damage are determined by the ratio between the size of fine fractions in fracturing fluid residue and the pore-throat size in experiments.Poor physical properties(K<0.5 mD)result in a more preferential flow pathway effect during flowback,and the stepwise incremental pressure differential proves to be more effective for the discharge of fracturing fluid in submicron pore throats.The permeability is significantly influenced by the differential distri-bution of retained fracturing fluid,as supported by direct experimental evidence.The presence of good physical properties(K>0.5 mD)combined with a scattered distribution of retained fracturing fluid is associated with high gas phase recovery permeability,whereas a continuous sheet-like distribution results in low recovery permeability.The expansive surface area and presence of filamentous illite minerals facilitate the multiple winding and adsorption of fracturing fluids,demonstrating strong hydrogen-bonding,multi-layering and multiple adsorption properties.The geological characteristics of the main gas formations exhibit significant variation,and the severity of damage caused by fracturing fluids occurs in diverse sequences.To address this issue,a differentiated strategy for optimizing frac-turing fluids has been proposed.展开更多
Pores and fractures are important components of flow channels in coal-measure gas reservoirs.While considerable studies have been conducted on pore structure evolution,very few studies have investigated the fracture d...Pores and fractures are important components of flow channels in coal-measure gas reservoirs.While considerable studies have been conducted on pore structure evolution,very few studies have investigated the fracture distribution and self-similarity characteristics.To reveal the characteristics of fracture distribution in coal and shale reservoirs,computed tomography studies were performed on 15 coal and shale samples from the Shanxi and Taiyuan formations.The results show that the fracture distribution of samples of the same lithology differs significantly,and the fracture distribution heterogeneity of shale samples is much higher than that of coal samples.In shale,the heterogeneity of fracture distribution is mainly caused by pores and fractures smaller than 2μm in the z-direction,with relatively little contributions from pores and fractures in the x and y directions.However,the heterogeneity of fracture distribution in coal is mainly controlled by pores and fractures larger than 2μm in all directions,and the difference between the three directions is minor.It was shown that a great number of microscopic pores and fractures contribute to the highest fractions of porosity in different lithological samples.This method is useful for determining the fracture distribution characteristics in shale and coal-measure gas reservoir.展开更多
基金supported by the Chinese National Science Foundation (51104147)the Fundamental Research Funds for the Central Universities (2011QNA17)+1 种基金National Basic Research Program of China (2010CB226800)State Key Laboratory for Geo-mechanics and Deep Underground Engineering in China
文摘The effect of the fracture distribution on CO 2 injection into coal seams was studied with a heterogeneous model having dual porosity to represent both the primary medium (the coal matrix) and the secondary medium (the fractures) under variable stress conditions. A numerical generation method and a digital image processing method were used to model the heterogeneous fracture distribution in the coal. The model solutions demonstrate that: (1) the fractures are the main channel for gas flow and their distribution has an important impact on the gas injection rate; (2) the fractures only affect the injection rate of CO 2 into the coal but not the final storage amount; (3) when gas is injected into coal the fractures will first expand and then close due to the changing effective stresses and the adsorption induced swelling of coal grains. This fully coupled dual-porosity model with a heterogeneous fracture distribution provides a way to predict the CO 2 injection into a coal seam.
基金financially supported by the National Natural Science Foundation of China (Grant No. 41521002 41130745+2 种基金 41272330)State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project (Grant No. SKLGP2016Z015)supported by the Funding of Science and Technology Office of Sichuan Province (Grant Nos. 2015JQ0020)
文摘Gently dipping fractures subjected to river incision are widely distributed on rock slopes.In this paper,a rock slope on the Nujiang River(China)is investigated to study the role of gently dipping fractures in the rock slopes evolution.Detailed field surveys indicate that gentle fractures are concentrated in four main zones.Moreover,the kinematics of the fracture system suggest that the genesis of these fractures can be synthesized into a progressive evolution model.This model indicates that the joints begin with the formation of an array of en echelon cracks that are subjected to continued crack elongation and shearing before ultimately approaching one another and interacting to form a complex joint system.Geomechanical analysis is performed to reveal the mechanisms of this genesis,and three main fracture patterns are identified based on the slope stress and are classified with respect to the slope evolution.Based on the detail field investigations and the evolutionary history of the river valley,we propose that intermittent incision by the river was the main factor contributing to the concentrated distribution of gently dipping joints.
基金granted by Petro China Major Science and Technology Project(Grant No.ZD2019-18301-003)Natural Science Foundation of Shandong Province(Grant No.ZR2023MD069)+1 种基金Training Program of Innovation for Undergraduates in Shandong Institute of Petroleum and Chemical Technology(Grant No.2022084)Science Development Foundation of Dongying(Grant No.DJ2020007)。
文摘The deep Lower Jurassic Ahe Formation(J_(1a))in the Dibei–Tuzi area of the Kuqa Depression has not been extensively explored because of the complex distribution of fractures.A study was conducted to investigate the relationship between the natural fracture distribution and structural style.The J_(1a)fractures in this area were mainly high-angle shear fractures.A backward thrust structure(BTS)is favorable for gas migration and accumulation,probably because natural fractures are more developed in the middle and upper parts of a thick competent layer.The opposing thrust structure(OTS)was strongly compressed,and the natural fractures in the middle and lower parts of the thick competent layer around the fault were more intense.The vertical fracture distribution in the thick competent layers of an imbricate-thrust structure(ITS)differs from that of BTS and OTS.The intensity of the fractures in the ITS anticline is similar to that in the BTS.Fracture density in monoclinic strata in a ITS is controlled by faulting.Overall,the structural style controls the configuration of faults and anticlines,and the stress on the competent layers,which significantly affects deep gas reservoir fractures.The enrichment of deep tight sandstone gas is likely controlled by two closely spaced faults and a fault-related anticline.
基金financially supported by National Basic Research Programs of China (No.2015CB654802 and No.2015GB118001)National Natural Science Foundation of China(Grant No.51471094)
文摘Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr＇s circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; （stress induced critical martensite transformation temperature） would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.
基金supported by the National Basic Research Program of China(No.2006CB601205)the National Natural Science Foundation of China(No.10672027)the Key Project of National Natural Science Foundation of China(No.90816025)
文摘Model I quasi-static nonlinear fracture of aluminum foams is analyzed by considering the effect of microscopic heterogeneity. Firstly, a continuum constitutive model is adopted to account for the plastic compressibility of the metallic foams. The yield strain modeled by a two- parameter Weibull-type function is adopted in the constitutive model. Then, a modified cohesive zone model is established to characterize the fracture behavior of aluminum foams with a cohesive zone ahead of the initial crack. The tensile traction versus local crack opening displacement relation is employed to describe the softening characteristics of the material. And a Weibull statistical model for peak bridging stress within the fracture process zone is used for considering microscopic heterogeneity of aluminum foams. Lastly, the influence of stochastic parameters on the curve of stress-strain is given. Numerical examples are given to illustrate the numerical model presented in this paper and the effects of Weibull parameters and material properties on J-integral are discussed.
基金supported by the National Natural Science Foundation of China(No.52174045)。
文摘Natural fractures(NFs)are common in shale and tight reservoirs,where staged multi-cluster fracturing of horizontal wells is a prevalent technique for reservoir stimulation.While NFs and stress interference are recognized as significant factors affecting hydraulic fracture(HF)propagation,the combined influence of these factors remains poorly understood.To address this knowledge gap,a novel coupled hydromechanical-damage(HMD)model based on the phase field method is developed to investigate the propagation of multi-cluster HFs in fractured reservoirs.The comprehensive energy functional and control functions are established,while incorporating dynamic fluid distribution between multiple perforation clusters and refined changes in rock mechanical parameters during hydraulic fracturing.The HMD coupled multi-cluster HF propagation model investigates various scenarios,including single HF and single NF,reservoir heterogeneity,single HF and NF clusters,and multi-cluster HFs with NF clusters.The results show that the HMD coupling model can accurately capture the impact of approach angle(θ),stress difference and cementation strength on the interaction of HF and NF.The criterion of the open and cross zones is not fixed.The NF angle(a)is not a decisive parameter to discriminate the interaction.According to the relationship between approach angle(θ)and NF angle(a),the contact relationship of HF can be divided into three categories(θ=a,θ<a,andθ>a).The connected NF can increase the complexity of HF by inducing it to form branch fracture,resulting in a fractal dimension of HF as high as2.1280 at angles of±45°.Inter-fracture interference from the heel to the toe of HF shows the phenomenon of no,strong and weak interference.Interestingly,under the influence of NFs,distant HFs from the injection can become dominant fractures.However,as a gradually increases,inter-fracture stress interference becomes the primary factor influencing HF propagation,gradually superseding the dominance of NF induced fractures.
基金The authors greatly appreciate the Key R&D Plan of Shandong Province(No.2021CXGC011203)the Shandong Province Housing and Urban Rural Construction Science and Technology Plan(No.2019-K7-12).
文摘Groundwater inflow constitutes a critical challenge in rock tunnel engineering.This study systematically investigates the coupled effects of fracture spatial distribution and rock matrix permeability on tunnel water inflow using a novel embedded discrete fracture model based method.A set of quadratic regression models is established to delineate the relationship between inflow rate and fracture distribution parameters over a wide range of fracture-to-matrix permeability ratios(kf/km).Results demonstrate that fracture aperture,spacing,and their interaction dominate the inflow across all permeability ratios.Analysis of variance further reveals a threshold-dependent behavior:coupled effects are significant below a critical kf/km value but decay markedly above it.This threshold decreases with larger aperture and increases with wider spacing,yet remains nearly independent of fracture dip angle.Moreover,when kf/km is below the threshold,aperture and spacing exert greater influence on tunnel inflow at lower permeability ratios,while kf/km gains influence under larger apertures and smaller spacings.Finally,a case study of Nanwan Tunnel shows that matrix permeability plays a dual role—increasing the mean inflow rate while reducing uncertainty from stochastic fracture distribution.
基金supported by the Sichuan Youth Science and Technology Innovation Research Team Project(No.2021JDTDO017)the open Fund(PLN2022-11)of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)+1 种基金Southwest Petroleum University Graduate Innovation Fund(No.2022KYCX021)Jian Tian would like to acknowledge the funding from the National Natural Science Foundation of China(52404023).
文摘To elucidate the adsorption characteristics and retention mechanisms of fracturing fluids in diverse clay minerals,we conducted on-line nuclear magnetic resonance(NMR)and atomic force microscopy(AFM)experiments.The depth and extent of solid phase damage are determined by the ratio between the size of fine fractions in fracturing fluid residue and the pore-throat size in experiments.Poor physical properties(K<0.5 mD)result in a more preferential flow pathway effect during flowback,and the stepwise incremental pressure differential proves to be more effective for the discharge of fracturing fluid in submicron pore throats.The permeability is significantly influenced by the differential distri-bution of retained fracturing fluid,as supported by direct experimental evidence.The presence of good physical properties(K>0.5 mD)combined with a scattered distribution of retained fracturing fluid is associated with high gas phase recovery permeability,whereas a continuous sheet-like distribution results in low recovery permeability.The expansive surface area and presence of filamentous illite minerals facilitate the multiple winding and adsorption of fracturing fluids,demonstrating strong hydrogen-bonding,multi-layering and multiple adsorption properties.The geological characteristics of the main gas formations exhibit significant variation,and the severity of damage caused by fracturing fluids occurs in diverse sequences.To address this issue,a differentiated strategy for optimizing frac-turing fluids has been proposed.
基金supported by the National Natural Science Foundation of China(Grant Nos.41972171 and 42172156)the Fundamental Research Funds for the Central Universities(No.2020CXNL11)+1 种基金the Graduate Innovation Program of China University of Mining and Technology(No.KYCX22_2604)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘Pores and fractures are important components of flow channels in coal-measure gas reservoirs.While considerable studies have been conducted on pore structure evolution,very few studies have investigated the fracture distribution and self-similarity characteristics.To reveal the characteristics of fracture distribution in coal and shale reservoirs,computed tomography studies were performed on 15 coal and shale samples from the Shanxi and Taiyuan formations.The results show that the fracture distribution of samples of the same lithology differs significantly,and the fracture distribution heterogeneity of shale samples is much higher than that of coal samples.In shale,the heterogeneity of fracture distribution is mainly caused by pores and fractures smaller than 2μm in the z-direction,with relatively little contributions from pores and fractures in the x and y directions.However,the heterogeneity of fracture distribution in coal is mainly controlled by pores and fractures larger than 2μm in all directions,and the difference between the three directions is minor.It was shown that a great number of microscopic pores and fractures contribute to the highest fractions of porosity in different lithological samples.This method is useful for determining the fracture distribution characteristics in shale and coal-measure gas reservoir.
