Varying-scale shale gas flow: Discrete fracture networks (DFN) based numerical simulation

摘要

The development of unconventional gas reservoirs represents totally distinctive characteristics as compared with its conventional counterparts. The prevailing commercial strategy of stimulating fractures to connect the matrix to wellbores results in an even more complicated shale gas flow behavior, in which matrix flow is fairly coupled with fracture flow. Numerous works have been contributed to unveil the underground shale gas production mechanisms. And some impressive progresses have been made in describing the complex subterranean shale gas flow, such as the introduction of discrete fracture network (DFN) from National Energy Technology Laboratory (NETL). However, none of them captures the varying-scale nature of the in-place gas flow in shale sediments. In this work, we try to fill this gap. Following the concept of DFN, we set up mathematical models for shale gas flow in matrix and fracture networks, and also for their mass transfer in between without neglecting its varying-scale nature. In addition, we also investigate comprehensively the impact of various effects and phenomena occurred in pore spaces during production course, such as adsorption and desorption on rock surfaces, gas slippage and Knudsen diffusion, and diffusion in bulk kerogen, on the overall shale gas production using our new model for a specific shale gas reservoir case study.