Abstract: In response to the insufficient understanding of multi-scale fluid flow behavior under fluid-solid coupling in shale reservoirs,stress sensitivity experiments and Biot coefficient measurements were employed to study the inherent characteristics of shale matrix and fractures and their sensitivity to stress respectively.The interactions between micro-scale seepage and macro-scale effective stress were analyzed.Based on the effective stress principle,mathematical models were established for shale reservoir matrix-fracture porosity and permeability under effective stress,and the impacts of various fluid-solid coupling parameters on multi-scale flow in shale reservoirs were analyzed.The results show that the average stress sensitivity coefficients of the matrix and fractures are 0.220 and 0.081 respectively,indicating the matrix is more stress-sensitive than fractures.The average Biot coefficients of the matrix and fractures are 0.310 and 0.710 respectively,indicating the matrix's Biot coefficient is smaller than that of the fractures,thus pore pressure in fracture-developed reservoirs has a non-negligible impact on reservoir productivity.The smaller the normal stiffness,elastic modulus,Poisson's ratio,and initial porosity,the larger the Biot coefficient,and the stronger the fluid-solid coupling interaction between the matrix and fracture network,resulting in more obvious permeability reduction.Gas desorption-induced expansion causes deformation of shale matrix grains,enhancing fluid-solid coupling in the matrix.In proppant-filled fractures,larger proppant size and more layers of sand increase the normal stiffness of fractures,thereby improving fracture flow conductivity and weakening fluid-solid coupling effects.The proposed seepage model more comprehensively considers the influence of fluid-solid coupling mechanical parameters and can more accurately analyze the impact of fluid-solid coupling on multi-scale seepage behavior in shale,greatly simplifying calculations and improving computation speed.The findings provide a theoretical basis for the effective development of shale reservoirs.

Key words: shale gas reservoir, multi-scale, fluid-solid coupling, stress sensitivity, permeability