From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi's effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a co...From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi's effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a coupled hydromechanical analysis to solve the seepage-deformation interaction problem was illustrated by examining the equations of static equilibrium among the effective stress, seepage force, pore-water pressure and total stress. The conceptual definition of stress variable that satisfies the principles of continuum mechanics is applied in the coupled hydromechanical analysis. It is shown that Terzaghi's effective stress is in fact not a stress variable under seepage conditions, and the seepage force acting on the soil skeleton cannot be viewed as a body force. This offers a clue to the underlying cause of a paradox between the real Pascal's hydrostatic state and the hydrostatic state predicted by a class of continuum hydromechanical theories.展开更多
The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to...The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.展开更多
For clarifying the inherent relation between relieving fracture closure and improving the EUR by adopting the pressure-control production system for shale gas fractured horizontal wells,and the significance of pressur...For clarifying the inherent relation between relieving fracture closure and improving the EUR by adopting the pressure-control production system for shale gas fractured horizontal wells,and the significance of pressure-control production for gas reservoir engineering,a dynamic formationefracture coupling prediction model for production performance of fractured horizontal wells was established and solved,with the finite conductivity fracture as basic flow unit and the variable stress sensitivity coefficient introduced.Through a comparison of the calculated results from the established model,classical model and numerical modeling by the Saphir software,the effect of characteristic parameters of stress sensitivity and pressure-control production system on the production performance of fractured horizontal wells was analyzed and verified in two wells.The results show that(1)the calculated results from the established model are basically consistent with those from the classical model and the numerical modeling by the Saphir software;(2)the existence of stress sensitivity makes the fracture conductivity decline with the production of gas wells,which leads to the decrease of cumulative gas production;the greater the stress sensitivity,the greater the decrease of cumulative gas production;(3)although the initial gas production and cumulative gas production of shale gas gained by the pressure-control production system are low compared with those by the pressure-release production system,the ultimate cumulative gas production is higher.Thus,it is more reasonable to adopt a long-term pressure-control production system for shale gas fractured horizontal wells.In conclusion,the research results provide a theoretical support for the popularization of pressure-control production system of shale gas wells.展开更多
基金Project(51278171)supported by the National Natural Science Foundation of ChinaProject(B13024)supported by the"111"Project,China+1 种基金Projects(2014B04914,2011B02814,2010B28114)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(617608)supported by the Research Grants Council of the Hong Kong Special Administrative Region of China
文摘From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi's effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a coupled hydromechanical analysis to solve the seepage-deformation interaction problem was illustrated by examining the equations of static equilibrium among the effective stress, seepage force, pore-water pressure and total stress. The conceptual definition of stress variable that satisfies the principles of continuum mechanics is applied in the coupled hydromechanical analysis. It is shown that Terzaghi's effective stress is in fact not a stress variable under seepage conditions, and the seepage force acting on the soil skeleton cannot be viewed as a body force. This offers a clue to the underlying cause of a paradox between the real Pascal's hydrostatic state and the hydrostatic state predicted by a class of continuum hydromechanical theories.
基金supported by National Natural Science Foundation of China(No.50675209)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China(No.200724).
文摘The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.
基金supported by the National Major Science and Technology Project“Zhaotong Shale Gas Exploration&Development Demonstration Project”(No.:2017ZX05063)“Characterization of Shale Gas Production Pattern and Optimization of Development Strategies”(No.:2017ZX05037-002).
文摘For clarifying the inherent relation between relieving fracture closure and improving the EUR by adopting the pressure-control production system for shale gas fractured horizontal wells,and the significance of pressure-control production for gas reservoir engineering,a dynamic formationefracture coupling prediction model for production performance of fractured horizontal wells was established and solved,with the finite conductivity fracture as basic flow unit and the variable stress sensitivity coefficient introduced.Through a comparison of the calculated results from the established model,classical model and numerical modeling by the Saphir software,the effect of characteristic parameters of stress sensitivity and pressure-control production system on the production performance of fractured horizontal wells was analyzed and verified in two wells.The results show that(1)the calculated results from the established model are basically consistent with those from the classical model and the numerical modeling by the Saphir software;(2)the existence of stress sensitivity makes the fracture conductivity decline with the production of gas wells,which leads to the decrease of cumulative gas production;the greater the stress sensitivity,the greater the decrease of cumulative gas production;(3)although the initial gas production and cumulative gas production of shale gas gained by the pressure-control production system are low compared with those by the pressure-release production system,the ultimate cumulative gas production is higher.Thus,it is more reasonable to adopt a long-term pressure-control production system for shale gas fractured horizontal wells.In conclusion,the research results provide a theoretical support for the popularization of pressure-control production system of shale gas wells.
