Performance analysis of a composite dual-porosity model in multi-scale fractured shale reservoir

Abstract The multiple mechanisms of adsorbed gas and free gas lead the complexity flow in shale porous media. Shale gas reservoirs exhibit stress sensitivity permeability characteristics that are expected to have a significant effect on well performance. Meanwhile, micro-seismic monitoring technology has demonstrated that hydraulic fracturing could create only a limited complex fracture network area around fractured horizontal wellbores in unconventional reservoirs, which is very complicated and is often overlooked in mathematical models. In this paper, we conduct a comprehensive consideration of gas flow in shale reservoirs to improve the performance analysis of multistage horizontal fractured wells (MFHW). To account for the quasi-steady cross-flow between fracture and matrix consisting of viscous flow and the steady adsorption and desorption process, a dual-porosity model is employed for a stimulated reservoir region. Specifically, the stress-sensitivity effect of a fracture system was considered. An unstimulated reservoir region follows the single-porosity medium, which represents sealed natural fractures. Duhamel's theorem, the perturbation method, the superposition principle, the numerical discrete method and the Stehfest numerical inversion algorithm are employed to obtain semi-analytical solutions of the composite model. According to type curves analysis, MFHW flow regimes are given to the flow patterns, and the basic flow regimes are categorized in terms of in which time region they occur. Furthermore, the sensitivity analysis of pressure responses and early transient flow curves, including stimulated reservoir volume (SRV), stress sensitivity, fracture half-length and Langmuir adsorption volume, are carefully studied. The composite model and results can be used to expand the analysis models for multistage fractured horizontal wells in shale gas reservoirs.