Performance Simulation Of Fractured Horizontal Wells In Shale Gas Reservoirs Considering Multi-field Coupling

Nowadays,shale gas development has become the key component of global unconventional oil and gas development.Scientific and efficient development of China's abundant shale gas resources can effectively alleviate the contradiction between energy supply and demand,and ensure the strategic safety of China's energy.Accurate understanding of gas seepage characteristics in shale gas development process,accurate simulation and prediction of production performance of fractured horizontal wells in shale gas reservoirs are of great significance for guiding efficient development of shale gas reservoirs.Based on the comprehensive consideration of multiple flow mechanism of shale gas in multi-scale reservoir space(viscous flow,Knudsen diffusion,surface diffusion,adsorption gas desorption,etc.),this paper establishes a comprehensive flow mathematical model of shale gas reservoir under the coupling of seepage field and stress field,considering the influence of stress field changes on rock porosity and permeability during production.On the basis of appropriate characterization of complex fracture network in volume fracturing,a numerical discrete model of multi-stage fractured horizontal wells in shale gas reservoirs which under the coupling of seepage field and stress field is established based on finite element-finite volume method.According to the numerical results,the production performance of fractured horizontal wells in shale gas reservoirs under the coupling of multi-field is simulated and analyzed.The main tasks completed are as follows:(1)The micro-seepage mechanism model of shale gas considering the coupling effects of seepage field(viscous flow,Knudsen diffusion,adsorbed gas desorption,Gas slippage effect)and stress field(the effect of rock deformation on porosity and permeability)is established.(2)The program which can generate meshing grid for discrete fracture model is developed,and the complex fracture mesh system in shale reservoir is appropriately characterized by unstructured triangular(tetrahedral)mesh.The comprehensive seepage mathematical model of multi-stage fractured horizontal wells in shale gas reservoir under the coupling of seepage field and stress field is established.The seepage numerical model of multi-stage fractured horizontal wells in shale gas reservoir is constructed based on finite element-finite volume theory.(3)The fully implicit iterative solution scheme of finite element-finite volume method for the seepage model of fractured horizontal wells in shale gas reservoirs under the coupling of stress field and seepage field is established,and the numerical model is developed and calculated in the MATLAB programming environment.(4)Based on the established mathematical and numerical model of fractured horizontal well in shale gas reservoirs,the production performance of fractured horizontal well is simulated,and the effects of adsorption gas desorption,stress sensitivity and permeability of natural fracture system in SRV region on the production performance of fractured horizontal wells are analyzed.It is found that under the assumption of a large number of natural fractures,the production of shale gas wells will be significantly reduced due to the stress sensitivity effect;the desorption of adsorbed shale gas will significantly affect the production performance of fractured horizontal wells in the middle and late stage of production.The physical parameters of micro-fracture system in SRV region have a great impact on the production of shale gas wells in the middle and early stages,while the physical parameters of matrix system mainly affect the production of shale gas wells in the late stage of production.The research results of this paper have formed a set of dynamic production simulation method for fractured horizontal wells in shale gas reservoirs under the coupling of seepage field and stress field,which has theoretical significance and practical value for guiding the rational development of shale gas.