High-Pressure Adsorption of Pure Coalbed Gases on Dry Coal Matrices

As part of our efforts to model enhanced coalbed methane recovery and CO2 sequestration in coalbeds, we have investigated the pure adsorption isotherm behavior of five dry coals namely, Illinois #6, Wyodak sub-bituminous, Pocahontas, Beulah Zap, and Upper Freeport coal. Using a volumetric technique, isotherms of pure methane, nitrogen, CO2 and ethane were measured at a temperature of 328.15 K (131°F) and pressures to 13.8 MPa (2000 psia). In most cases, the adsorption replicate isotherms were measured to ascertain the experimental reproducibility. Errors from primary pressure, temperature, and volume measurements were propagated to estimate the uncertainty of each adsorption datum point. On average, the expected experimental uncertainty of the pure-gas adsorption data is 7%. Ono-Kondo lattice model was used to represent the adsorption isotherms of the coals considered, and the model parameters were regressed for each coal. In general, the model represents the adsorption isotherms within their experimental uncertainties.