Quantitative study in shale gas behaviors using a coupled triple-continuum and discrete fracture model.

Abstract The shale has ultra-low permeability wherein multi-scale natural fractures are well-developed. The success of providing high diversion channels makes multi-stage fractured horizontal wells (MFHWs) become the powerful technique for economically producing gas from shale. This study presents a triple-continuum and discrete fracture model to describe a fractured shale reservoir embedded with a MFHW. The model incorporates non-equilibrium desorption/adsorption mechanism (NEDAM), viscous flow, Knudsen diffusion, and surface diffusion. The discrete fracture networks (DFNs) is quantitatively constructed according to the fracture density and stimulated reservoir area (SRA). This model is used to analyze the temporal/spatial evolution of the gas pressure and the net desorption rate. NEDAM is compared with the conventional equilibrium desorption mechanism (EDM) and it's found that NEDAM uncovers the delayed phenomenon during gas desorption, and the use of EDM overestimates the production contributed from the adsorbed gas. The maximum net desorption rate of adsorbed gas gradually spread from the SRA region to the non-SRA region. The complete flow stages are clearly interpreted in a semi-logarithmic curve of well testing, and the flow stage controlled by the hydraulic fractures is clearly presented. Finally, the instructions on hydraulic fracturing treatment are given based on the production analysis. Highlights • This paper presents a hierarchical approach which integrates DFNs with multi-continuum concept to model various coupling mechanisms of gas nonlinear transport in shale. • By introducing the concepts of stimulated reservoir area (SRA) and fracture density, the HFNs are quantitatively generated with stochastic algorithms. • Non-equilibrium desorption/adsorption mechanism uncovers the delayed phenomenon during gas desorption, and the maximum net desorption rate of adsorbed gas gradually spread from the SRA region to the non-SRA region. • There are critical values of the flow conductivities of main fracture and secondary fractures as to improve the shale gas production. [ABSTRACT FROM AUTHOR]