Measurement and evaluation of coal sorption isotherm data

Abstract

The proper measurement and interpretation of sorption isotherm data is of primary importance in understanding and predicting the gas production performance of a coalbed methane reservoir. These data are used to predict the release of gas from the reservoir as the pressure is reduced during production and the eventual gas recovery (reserves). A sorption isotherm is a laboratory measurement performed on a representative coal sample to determine the methane storage capacity as a function of pressure. The term 'isotherm' results as the experiment is performed at a constant temperature which should be equal to that of the reservoir. This paper presents the use of the data, procedures for performing the measurements, a methodology for interpreting the experimental data for estimates of gas storage capacity and diffusion coefficients of the coal matrix, and isotherms obtained from a variety of coal samples.