Mathematical Model of Shale Gas Reservoirs Coupled by Desorption,Stress Sensitivity and Fractures Finite Conductivity

摘要

The characteristic and simulation of shale gas reservoir are hotspot in the aspect of flow study in porous and fractured media. Previous shale-gas reservoir modeling work has largely neglected the affect of gas desorption and stress dependent fracture permeability on well productivity and gas recovery. In this paper, a new simulation model for shale gas reservoir is presented based on the dual-porosity and dual-permeability model, which considers absorption, desorption, diffusion, convection and solid deformation. For the horizontal fractured well, gas flow is considered as finite conductivity from ultra low permeability rock through the primary hydraulic fracture to the borehole and pressure drop is from friction and acceleration in the horizontal well bore and primary hydraulic fracture. This mathematical model is discrete and solved by numerical method and is used to an example horizontal well of shale-gas reservoir to analyze the impact of gas desorption and stress sensitivity on cumulative gas production. The results show gas desorption significantly affects the later well production and the stress sensitivity could affect the fracture permeability in the later depletion production and could decrease gas recovery by 8%.