Coal was considered rock matrix-fractured media composed of rock matrix and fractures, and the rock matrix-fractured media model for heterogeneous and fractured coal bed was presented. In this model the rock matrix is...Coal was considered rock matrix-fractured media composed of rock matrix and fractures, and the rock matrix-fractured media model for heterogeneous and fractured coal bed was presented. In this model the rock matrix is heterogeneous, and the mechanical parameters such as elastic modulus and strength follow Weibull distribution. Fractures in coal bed were generated with the discrete fracture network method, and the properties of fractures were simulated with Desai element. Then the virtual generating system (VGS) of natural heterogeneous and fractured coal bed was developed in Matlab 6.0. The coupled model of gas flow and deformation process based on the rock matrix-fractured media model method and VGS for heterogeneous and fractured coal bed was presented, and the numerical code was developed in Matlab 6.0. The gas flow process in the heterogeneous and fractured coal bed was simulated in a numerical case. The main conclusions are: 1) The natural heterogeneous and fractured coal bed could be simulated by the rock matrix-fractured media model and VGS; 2) The fractures connected with the well have much more effects on gas flow than those non-connected.展开更多
Gas transport in coal induces effective stress variation,matrix swelling/shrinkage,and significantly affects matrix and fracture deformation,resulting in porosity and permeability evolution.However,the heterogeneity a...Gas transport in coal induces effective stress variation,matrix swelling/shrinkage,and significantly affects matrix and fracture deformation,resulting in porosity and permeability evolution.However,the heterogeneity and anisotropy of coal are neglected in dual porosity models,which can lead to the deviation from the real physical mechanisms.To uncover the permeability evolution,especially the influence of dynamic matrix-fracture interaction for real fracture distribution,advanced virtual simulation is proposed.In this study,real fracture geometry is taken into account in the physical model based on the CT-scan image,while the mathematical models for coal deformation and gas flow are established.Our calculations are verified against a long-term experimental data under the same boundary condition.Accordingly,the real matrix-fracture interaction caused by adsorption-induced matrix deformation has been visually exhibited,and some new insight into the behavior of fracture permeability in real materials is offered.The results indicate the non-uniform distribution of fracture geometry is responsible for the nonmonotonic change of permeability.It also found that injection pressure,Langmuir strain constant and initial matrix permeability have important influences on the fracture permeability evolution.This research provides valuable insight into the understanding of the permeability change for the real fracture spatial distribution in coal.展开更多
Tight oil resources are abundant in the world.It is very important to strengthen the research on the development theory and technology of tight oil reservoirs for ensuring national energy security.Natural gas huff-n-p...Tight oil resources are abundant in the world.It is very important to strengthen the research on the development theory and technology of tight oil reservoirs for ensuring national energy security.Natural gas huff-n-puff can effectively improve the oil recovery of tight oil reservoirs.However,the pore-scale oil production characteristics and the mechanisms of natural gas huff-n-puff in matrix-fracture cores are poorly understood.The influence degree of important factors on oil recovery is not clear and the interactions between factors are rarely considered.In this paper,the oil production characteristics and mechanisms of natural gas huff-n-puff in tight cores with different fracture lengths were quantitatively analyzed by combining nuclear magnetic resonance(NMR)with numerical simulation technology.The influencing factors and their interactions were evaluated by the response surface method(RSM).The results show that tight cores mainly consist of medium pores(0.1–1μm)and small pores(0.01–0.1μm).The fracture mainly increases the proportion of macro-pores(1–10μm)and medium pores.In the natural gas huff-n-puff process,crude oil from macro-pores(1–10μm)and medium pores is mainly developed,and the contribution percentage of crude oil in medium pores to oil recovery is the largest,up to 98.28%.The position of gas–oil contact(GOC)moves deeper as the number of huff-n-puff cycles increases.The contents of CH_(4) and CO_(2) in the oil phase remain at a high level within the GOC,while between the GOC and the component sweep front,the contents of CH_(4) and CO_(2) in the oil phase decrease with the increase in dimensionless distance.The gas component sweep volume is increasing with the increase in fracture length.Moreover,the injected natural gas mainly extracts C_(3)–C_(10) components from crude oil.The reduction law of crude oil viscosity is consistent with the migration laws of CH_(4) components along the path.Compared with soaking time and gas diffusion coefficient,the injection pressure is the most significant factor underlying the recovery of natural gas huff-n-puff in tight cores.Besides the influence of single-factor,the interaction effects of gas injection pressure and diffusion also should be considered to determine the huff-n-puff parameters in the field implementation of natural gas huff-n-puff in tight reservoirs after fracturing.展开更多
Coal bed methane(CBM),the high-quality and efficient fuel,has caught the interest of many nations as they strive for environmentally friendly development.Therefore,the efficient exploitation and utilization of CBM has...Coal bed methane(CBM),the high-quality and efficient fuel,has caught the interest of many nations as they strive for environmentally friendly development.Therefore,the efficient exploitation and utilization of CBM has become one of the international focal research problems.A significant factor affecting the mining of CBM is coal permeability.To better capture the changes that occur during the extraction of CBM,the internal swelling coefficient of matrix(ISCM)has been gradually in permeability introduced into the permeability models,and such models have become an important type of the development of permeability models.The goal is to find out more precisely the evolution mechanism of the ISCM and its influence on the permeability models.In this paper,the selection of coal structure,determination of boundary conditions and influencing factors of permeability for were first analyzed.Then,according to the research process of ISCM,the permeability models including the ISCM were reviewed and divided into four phases:proposal phase,development phase,evaluation phase and display of internal structure phase.On the basis of the ISCM values in the current coal permeability models,the primary influencing factors and evolutionary laws of the ISCM are explored.The results obtained provide guidance for future theoretical refinement of permeability models with the ISCM.展开更多
基金Projects(50874064,50804026)supported by National Natural Science Foundation of ChinaProject(E2011208036)supported by the Natural Science Foundation of Hebei Province,China
文摘Coal was considered rock matrix-fractured media composed of rock matrix and fractures, and the rock matrix-fractured media model for heterogeneous and fractured coal bed was presented. In this model the rock matrix is heterogeneous, and the mechanical parameters such as elastic modulus and strength follow Weibull distribution. Fractures in coal bed were generated with the discrete fracture network method, and the properties of fractures were simulated with Desai element. Then the virtual generating system (VGS) of natural heterogeneous and fractured coal bed was developed in Matlab 6.0. The coupled model of gas flow and deformation process based on the rock matrix-fractured media model method and VGS for heterogeneous and fractured coal bed was presented, and the numerical code was developed in Matlab 6.0. The gas flow process in the heterogeneous and fractured coal bed was simulated in a numerical case. The main conclusions are: 1) The natural heterogeneous and fractured coal bed could be simulated by the rock matrix-fractured media model and VGS; 2) The fractures connected with the well have much more effects on gas flow than those non-connected.
基金supported by National Key Research and Development Program of China(2020YFA0711802)the China Postdoctoral Science Foundation(2019M661997)+3 种基金the National Natural Science Foundation of China(51774277)the Australian Research Council under Grant(DP200101293)the Science and Technology Major Project of Shanxi Province,China(20201102001)the Open Fund of State Key Laboratory of Coal and CBM Co-Mining(2018KF09)。
文摘Gas transport in coal induces effective stress variation,matrix swelling/shrinkage,and significantly affects matrix and fracture deformation,resulting in porosity and permeability evolution.However,the heterogeneity and anisotropy of coal are neglected in dual porosity models,which can lead to the deviation from the real physical mechanisms.To uncover the permeability evolution,especially the influence of dynamic matrix-fracture interaction for real fracture distribution,advanced virtual simulation is proposed.In this study,real fracture geometry is taken into account in the physical model based on the CT-scan image,while the mathematical models for coal deformation and gas flow are established.Our calculations are verified against a long-term experimental data under the same boundary condition.Accordingly,the real matrix-fracture interaction caused by adsorption-induced matrix deformation has been visually exhibited,and some new insight into the behavior of fracture permeability in real materials is offered.The results indicate the non-uniform distribution of fracture geometry is responsible for the nonmonotonic change of permeability.It also found that injection pressure,Langmuir strain constant and initial matrix permeability have important influences on the fracture permeability evolution.This research provides valuable insight into the understanding of the permeability change for the real fracture spatial distribution in coal.
基金supported by the National Natural Science Foundation of China(Grant No.U22B6004,51974341,51904324)the Fundamental Research Funds for the Central Universities(No.20CX06070A)the Science and Technology Support Plan for Youth Innovation of University in Shandong Province(Grant No.2019KJH002).
文摘Tight oil resources are abundant in the world.It is very important to strengthen the research on the development theory and technology of tight oil reservoirs for ensuring national energy security.Natural gas huff-n-puff can effectively improve the oil recovery of tight oil reservoirs.However,the pore-scale oil production characteristics and the mechanisms of natural gas huff-n-puff in matrix-fracture cores are poorly understood.The influence degree of important factors on oil recovery is not clear and the interactions between factors are rarely considered.In this paper,the oil production characteristics and mechanisms of natural gas huff-n-puff in tight cores with different fracture lengths were quantitatively analyzed by combining nuclear magnetic resonance(NMR)with numerical simulation technology.The influencing factors and their interactions were evaluated by the response surface method(RSM).The results show that tight cores mainly consist of medium pores(0.1–1μm)and small pores(0.01–0.1μm).The fracture mainly increases the proportion of macro-pores(1–10μm)and medium pores.In the natural gas huff-n-puff process,crude oil from macro-pores(1–10μm)and medium pores is mainly developed,and the contribution percentage of crude oil in medium pores to oil recovery is the largest,up to 98.28%.The position of gas–oil contact(GOC)moves deeper as the number of huff-n-puff cycles increases.The contents of CH_(4) and CO_(2) in the oil phase remain at a high level within the GOC,while between the GOC and the component sweep front,the contents of CH_(4) and CO_(2) in the oil phase decrease with the increase in dimensionless distance.The gas component sweep volume is increasing with the increase in fracture length.Moreover,the injected natural gas mainly extracts C_(3)–C_(10) components from crude oil.The reduction law of crude oil viscosity is consistent with the migration laws of CH_(4) components along the path.Compared with soaking time and gas diffusion coefficient,the injection pressure is the most significant factor underlying the recovery of natural gas huff-n-puff in tight cores.Besides the influence of single-factor,the interaction effects of gas injection pressure and diffusion also should be considered to determine the huff-n-puff parameters in the field implementation of natural gas huff-n-puff in tight reservoirs after fracturing.
基金Financial support is provided by the Research Funds for Key Laboratory of Safe and Effective Coal Mining(Anhui University of Science and Technology)Ministry of Education(JYBSYS2021209)+2 种基金National Science Foundation of China(51804176,51974169 and 51904270)Natural Science Foundation of Shandong Province(ZR2023ME031 and ZR2020QE124)China Postdoctoral Science Foundation(2019M652346 and 2018M 642632).
文摘Coal bed methane(CBM),the high-quality and efficient fuel,has caught the interest of many nations as they strive for environmentally friendly development.Therefore,the efficient exploitation and utilization of CBM has become one of the international focal research problems.A significant factor affecting the mining of CBM is coal permeability.To better capture the changes that occur during the extraction of CBM,the internal swelling coefficient of matrix(ISCM)has been gradually in permeability introduced into the permeability models,and such models have become an important type of the development of permeability models.The goal is to find out more precisely the evolution mechanism of the ISCM and its influence on the permeability models.In this paper,the selection of coal structure,determination of boundary conditions and influencing factors of permeability for were first analyzed.Then,according to the research process of ISCM,the permeability models including the ISCM were reviewed and divided into four phases:proposal phase,development phase,evaluation phase and display of internal structure phase.On the basis of the ISCM values in the current coal permeability models,the primary influencing factors and evolutionary laws of the ISCM are explored.The results obtained provide guidance for future theoretical refinement of permeability models with the ISCM.
