| There are abundant oil and gas resources in marine carbonate reservoirs of China,which are mainly characterized by fractured vuggy formations.Fractured vuggy carbonate reservoirs have strong heterogeneity and various pore spaces,including fractures,dissolved pores and vugs.The fluid flow in such media is complex due to the coexistence of porous flow in matrix and fractures and free flow in vugs.Moreover,the depth of fractured vuggy carbonate reservoirs is commonly large(more than 5000 m),and the formation suffers high temperature,high pressure and high in-situ stress.The deformation of fractures and vugs has great influence on the fluid flow during depletion,leading to significant hydro-mechanical coupling effect.The existing theories and numerical simulation methods are not well applicable for fractured vuggy carbonate reservoirs.Therefore,it is necessary to develop the numerical simulation method and technique to effectively characterize the complex flow patterns and hydro-mechanical coupled process in fractured vuggy carbonate reservoirs.In this dissertation,we firstly proposed a coupled flow and geomechanics model for fractured vuggy carbonate reservoirs.For fluid flow,the multiphase multicomponent model is adopted to handle the complex phase behaviors in fractured vuggy carbonate reservoirs.The multiphase Darcy’s law is used to describe fluid flow in matrix and fractures,and the multiphase free flow in vugs is reasonably simplified with the assumption of instantaneous gravity segregation.For deformation,the stress equation of fractured vuggy reservoirs is derived by considering the elastic deformation of matrix,nonlinear fracture closure and shear dilation effect,and vug deformation.Then to discretize the fractured vuggy porous media with complex geometries,we developed three kinds of gridding techniques,i.e.,discrete fracture-vug model based unstructured conformal grid,embedded discrete fracture-vug model based structured unconformal grid,and improved embedded discrete fracture-vug model based corner-point grid,to meet the demands of different research problems.The flow and mechanical equations are discretized by using finite volume method and finite element method,respectively.Then the fixed-stress splitting method is used to iteratively solve the coupled flow and geomechanics problem.The hydro-mechanical coupled numerical simulator for fractured vuggy reservoirs is developed,which is verified by a series of examples.Finally,based on the developed hydromechanical coupled simulator,three application studies are conducted.The coupled flow and geomechanical behaviors of fractured vuggy porous media and the sensitivity studies are firstly investigated,in which the significant effect of fracture shear dilation on hydro-mechanical coupling behaviors of natural fracture network,and the dominate effect of vugs on fluid flow and deformation of fractured vuggy porous media are revealed.Then the production patterns of different typical fracture-vug unit models for oil and condensate gas reservoirs are analyzed,based on which the effect of fracture-vug configuration on production is deeply understood.Finally,the applicability of the developed simulator on real oilfield problems are tested through the simulation cases of complex fractured vuggy carbonate oil reservoirs of Tarim and Tahe oilfields.In summary,the efficient coupled flow and geomechanics mathematical theory and numerical simulation method for fractured vuggy carbonate reservoirs are propsed in this dissertation.A hydro-mechanical coupled numerical simulator for fractured vuggy reservoirs is developed,which is applied in Tarim and Tahe oilfields and provides theoretical basis and technical support for the efficient development of fractured vuggy carbonate reservoirs. |
