Study Of Geomechanical Coupled Seepage Theory And Flow Simulation Of Tight Gas Reservior

As an unconventional natural gas resource,tight gas has huge resources in China,and its output accounts for the increasing proportion of total natural gas production in China.The tight gas reservoir has the characteristics of poor physical property,low porosity and low permeability and fracture development.The reservoir physical property changes with the change of Geostress in the development process of gas reservoir,which is manifested in rock deformation,fracture closure,reservoir porosity and permeability stress sensitive effect.In the study of the seepage theory of tight gas reservoir,the stress sensitive equation and the porosity and permeability dynamic model are only a single function of pressure,ignoring the effect of rock deformation on the gas seepage,and this effect has been proved to not be negligible in other unconventional gas reservoirs.Based on this research background,this paper studies the seepage theory of tight gas reservoir under the coupling of geomechanics.The related research not only can theoretically explore the influence of various geomechanics effects on rock deformation and reservoir physical parameters in the development process of tight gas reservoir,but also can guide the efficient development of gas reservoir.Based on the research goal of this paper,the following works are mainly carried out.(1)Based on the elastoplastic theory of porous media,the stress field control equation of tight reservoir deformation in the process of gas flow in homogeneous and double medium tight gas reservoirs is established.(2)Considering the influence of geostress on the physical parameters of tight gas reservoirs,based on the elastoplastic theory of porous media and the mechanism of matrix and fracture deformation,the dynamic model of porosity and permeability of tight reservoir cracks and matrix is established respectively.(3)Based on the mathematical model established by(2),the governing equations of gas reservoir seepage in homogeneous and double medium tight gas reservoirs are established in consideration of the continuity equation of gas flow and the mass conservation equation.(4)On the basis of(1)and(3),a mathematical model for the coupling of single phase gas seepage in tight reservoir with stress field and seepage field is established.Based on Matlab and COMSOL Multiphysics platform for secondary development,the multi field coupling mathematical model is solved by finite element method,and the multi-field coupling mathematical simulation method of tight gas reservoir is formed.Based on this method,the numerical simulation for production process of vertical,horizontal and fractured horizontal wells in tight gas reservoir is carried out,and the influence of matrix permeability,fracture conductivity and fracture number on the production of tight gas reservoir is emphatically analyzed.This paper further perfects the study on the seepage theory of tight gas reservoir under the coupling of geomechanics.The results can be applied to analyze the changes of rock deformation,reservoir permeability and other parameters considering the effects of these parameters on the production process of tight gas reservoirs,and conclusions present certain significance for the development of tight gas reservoirs and benefits to oilfield production guidance.