Numerical simulation and production decline analysis of multiply fractured horizontal wells in shale gas reservoirs

Abstract

Multiply fractured horizontal wells (MFHWs) have been widely applied into shale gas production recently. Thus, analyzing well performances, in particular of production decline analysis of MFHWs is important for exploiting shale gas reservoirs effectively. There are various analytical and numerical methods which have been employed to investigate pressure transient or well productivity of MFHWs in shale reservoirs. However, most of them are not good enough to accurately predict fluid flow behaviors of shale gas by applying the modified Darcy’s law and oversimplified facture models. Based on the Dusty-Gas Model and Langmuir isotherm equation, a set of equations that can govern gas flow in shale matrix is firstly derived in this work. In these equations, desorption of adsorbed gas, diffusion and convective flow are considered. A numerical model is constructed by applying the perpendicular bisection (PEBI) grids to discretize the flowing equations. This model is proposed to investigate the effects of hydraulic fractures and shale reservoir properties on gas production. The simulation results show that (1) desorption of adsorbed gas increases the gas rate and prolongs each flow period, (2) diffusivity and matrix permeability mainly affect the appearance of compound linear flow period, (3) the larger the simulation reservoir volume is, the longer the formation linear flow lasts. In addition, this study also indicates that the optimized number of fractures and fractures with larger conductivity leads to increased well production. The proposed numerical model presents a new way to numerically simulate and analyze the production decline of multiply fractured horizontal shale gas wells.