Pore-Scale Permeability Characteristics of Deep Coalbed Methane Reservoirs

Abstract

Deep coalbed methane (CBM) reservoirs are accompanied by the fracture development, effectively revealing the influence of fracture morphology on reservoir permeability, which is crucial for predicting the comprehensive gas production performance of reservoirs. In this study, with microfocus CT and digital core reconstruction technology, 16 cores with different fracture apertures are reconstructed. The results show that coal samples from the Daning-Jixian block are predominantly calcite and easily hydrated, with accompanying gangue and typical fracture surfaces at interfaces. As fracture aperture increases, permeability rises exponentially. The K-Df and K-b permeability models were proposed, suitable for fractured cores with aperture <210 and >210 μm, respectively. Larger apertures expand the seepage pressure field, increasing pressure gradients in narrow areas, and when the aperture <200 μm, uneven low-pressure zones occur, but when >200 μm, more streamlines penetrate fractures, increasing velocities.