Numerical investigation of seepage characteristics of propped fracture in coalbed methane reservoirs

Abstract

The investigation of the pore structure characteristics and the effect on fluid seepage in propped fractures are important considerations for improving coalbed methane (CBM) production and optimizing CBM extraction systems. In this paper, a numerical model was established to study the pore structure characteristics and distribution of fluid pressure, velocity and pathline fields of propped fractures. The results showed that, with the increase of the closure stress, the porosity decreased linearly while the effective pore connectivity ratio first increased, then decreased. The best flow conductivity of the fracture was achieved at the closure stress of 12.67 MPa. In addition, there were disparities in the pore distribution of the different layers due to the uneven transfer of the closure stress from top to bottom. Compared to the top and bottom layers, the effective pore connectivity ratio and fluid pressure were significantly smaller in the middle layer, while the flow velocity and pathline length were larger. The top and bottom layers were the main fluid seepage channels. The results of this study can provide a theoretical basis for CBM production prediction and real-time quantitative optimization of CBM extraction systems.