Pressure transient analysis of multiple fractured horizontal well in composite shale gas reservoirs by boundary element method

The composite shale gas reservoir consists of an inner and an outer region. Inner region is stimulated reservoir volume (SRV) and contains shale matrix and natural fractures. Outer region represents un-stimulated reservoir volume (USRV) and contains shale matrix only. The interface boundary between SRV and USRV is often arbitrarily shaped rather than the regular, which can be derived from micro-seismic events of shale gas reservoirs with multiple fractured horizontal well (MFHW) Considering arbitrary interface boundary between SRV and USRV and outer boundary, a composite model is presented for MFHW in composite shale gas reservoirs, which based on multiple mechanisms, including adsorption/desorption, viscous flow, diffusive flow and stress sensitivity of natural fractures. Boundary element method (BEM) is introduced to solve the pressure response of MFHW in composite shale gas reservoirs. The accuracy of this model is validated by comparing its pressure response solution with the result derived from an analytical and a numerical method, respectively. According to pressure performance analysis of MFHW in composite shale gas reservoirs, eight flow regimes are identified: the early linear flow, the early radial flow, the second linear flow, the second radial flow, inter-porosity flow from shale matrix to natural fractures, the transition flow, diffusive flow and the third radial flow. The effects of relevant parameters on pressure response are analyzed, including mobility ratio, storability ratio, inter-porosity coefficient, diffusion coefficient, adsorption index and the shape of interface boundary. The result shows that BEM can be perfectly used to analyze the pressure performance of MFHW of composite shale gas reservoirs with arbitrary shaped interface boundary and outer boundary; the presented model can be used to interpret pressure data more accurately for shale gas reservoirs and provide more accurate dynamic parameters which are important for efficient reservoir development.