Study On Coupled Model Of Two-Phase Seepage Flow In Shale Reservoir And Two-Phase Bubble Flow In Horizontal Wellbore Of Fracturing Flowback Fluid

The development of shale gas reservoir requires large-scale hydraulic fracturing technology,which is likely to bring a series of pollution problems.The research on the specific flowback situation of flowback fluid in shale gas well is the premise to solve the pollution problems.At present,the research on fracturing flowback of shale gas well is mainly focused on single-phase flowback,but this thesis aims to study the dynamic process of shale gasfracturing flowback liquid in the pre-middle stage of fracturing flowback in matrix system,natural fracture system,vertical artificial fracture and horizontal wellbore.The specific research contents of this thesis are as follows:(1)Based on the mass conservation equation,considering the adsorption and desorption of shale gas in shale matrix,diffusion slippage,the number of vertical artificial fractures,the length of fractures,the spacing of fractures,and the interaction between multiple fractures,a two-phase seepage coupled model of shale gas and fracturing flowback liquid in shale reservoir is established.(2)Based on the homogeneous flow model and the law of conservation of mass and momentum,a two-phase bubble flowback model of shale gas-fracturing flowback liquid in horizontal wellbore of shale gas reservoirs is established by considering the influence of multiple non-equidistance vertical artificial fractures flowing into the wellbore.Then,the coupled model of gas-liquid two-phase seepage in shale reservoir and two-phase bubble flow in horizontal wellbore is obtained by coupling the two models established above.(3)By introducing dimensionless variables,the two-phase seepage model of shale gas and frac flowback liquid in shale matrix-natural fractures is transformed into a definite solution problem of partial differential equation.Then,mathematical methods such as Laplace transformation method,Gaver-Stehfest numerical inversion method,recursion method and iteration method are used to solve the coupled model of two-phase seepage flow in shale reservoir and two-phase bubble flow in horizontal wellbore of shale gas-fracturing flowback liquid,and the numerical algorithm is designed to solve this coupled model,and the pressure curve is drawn to verify the rationality of this model.The coupled model of two-phase seepage flow in shale reservoir and two-phase bubble flow in horizontal wellbore of shale gas-fracturing flowback liquid established in this thesis effectively reflects the whole dynamic process of shale gas-fracturing flowback liquid after hydraulic fracturing in shale gas reservoir development.The study in this thesis provides some theoretical support for the study of instantaneous concentration of pollutants in the flowback process of fracturing flowback fluid.