Multi-scale modelling of gas transport and production evaluation in shale reservoir considering crisscrossing fractures

Abstract

Advancements in recent shale gas development technologies like creating hydraulic fracturing have greatly improved the production of unconventional shale gas reservoirs (USGR). However, the production of USGR is still low mainly due to the inefficient gas transport in tight shale formation. Towards this end, the investigations about the mechanism of gas transport through the fractures and the effects of both hydraulic and natural fractures on the overall gas production are urgently needed. In this study, a multi-scale modelling is established to analyze the gas transport and production performance in shale formation with crisscrossing natural fractures using finite element method (FEM). For the base case with fracture-scale model, the gas transport behavior and pressure distribution within the matrix and crisscrossing fractures are revealed, demonstrating that the crisscrossing fractures serve as the fast paths to enhance the gas transport from shale matrix to wells. Then, the field-scale model is developed by considering the complex fracture networks consisting of the hydraulically fractured horizontal wells and crisscrossing natural fractures, which is well verified against field data. On this basis, the comprehensive analysis for the influence of various parameters, including the properties of matrix, hydraulic fractures and natural fractures, on the production performance are conducted to optimize the exploitation strategy of shale gas reservoir. It is believed that the multi-scale simulation framework and the optimized exploitation strategies presented in this study are useful for the enhanced gas recovery (EGR) of shale reservoir.