Prediction of Coalbed Methane (CBM) Production Considering Bidisperse Diffusion: Model Development, Experimental Test, and Numerical Simulation

Abstract

Gas flow in coal seam consists of laminar flow through coal cleat and diffusion through pores of coal matrix. Previous studies on the prediction of CBM production mostly focused on the impact of permeability change while the gas exchange between matrix and cleat was assumed to obey unipore diffusion assumption with a single diffusion coefficient. However, numerous scholars have found that a single diffusion coefficient cannot reproduce the sorption kinetic data precisely for a lot of coals, while bidisperse diffusion with fast and slow diffusion coefficients can represent the diffusion process well. Until now, attempts on studying the impact of bidisperse diffusion on CBM production are very limited and mathematical model describing the gas flow with bidisperse diffusion is unavailable. In this study, we propose a fully coupled coal seam gas flow model with consideration of bidisperse diffusion and the interaction between bidisperse diffusion, adsorption strain and geomechanical response of coal. A series...