Article pubs.acs.org/EF
Estimation of Pressure-Dependent Diffusive Permeability of Coal Using Methane Diffusion Coefficient: Laboratory Measurements and Modeling Yi Wang and Shimin Liu* Department of Energy and Mineral Engineering, G3 Center and Energy Institute, The Pennsylvania State University, University Park, Pennsylvania-16802, United States ABSTRACT: Gas diffusion in coal is critical for the prediction of coalbed methane (CBM) production, especially for the latestage CBM reservoir when both gas pressure and permeability are relative low. Using only Darcy permeability to evaluate the quality of gas transport might not be effective. Diffusive flow can be the dominant flow at low reservoir pressures. In this work, the methane diffusion coefficient was measured for pulverized San Juan sub-bituminous and Pittsburgh bituminous coal samples using the classic unipore model and particle method. The diffusion coefficient results showed a negative correlation with pressure, as reported previously. The significance of diffusion flow is strongly related to the rate of the methane ad-/desorption process, more severely in the low pressure range [
