Numerical Investigation of Multistage Fractured Horizontal Wells considering Multiphase Flow and Geomechanical Effects

Hydraulic fracturing is a key technology in unconventional reservoir production, yet many simulators only consider the single-phase flow of shale gas, ignoring the two-phase flow process caused by the retained fracturing fluid in the early stage of production. In this study, a three-dimensional fluid-gas-solid coupling reservoir model is proposed, and the governing equations which involve the early injection water phenomenon and stress-sensitive characteristics of shale gas reservoirs are established. The finite element-finite difference method was used for discretisation of stress and strain equations and the equations of flow balances. Further, a sensitivity analysis was conducted to analyse fracture deformation changes in the production. Fracture characteristics under different rock mechanics coefficients were simulated, and the influence of rock mechanics parameters on productivity was further characterised. The stimulated reservoir volume zone permeability could determine the retrofitting effect, the permeability increased from 0.02 to 0.1mD, and cumulative gas production increased from 18.08 to 26.42 million m(3), thus showing an increase of 8.34 million m(3), or 46%. The effect of Young's modulus on the yield was smaller than Poisson's ratio and the width and length of the fractures. Production was most sensitive to the length of the fractures. The length of the fracture increased from 200 to 400m, and the cumulative gas production increased from 26.44 to 38.34 million m(3), showing an increase of 11.9 million m(3), or 45%. This study deepens the understanding of the production process of shale gas reservoirs and has significance for the fluid-gas-solid coupling of shale gas reservoirs.