METHANE CAPACITIES OF BOWEN BASIN COALS RELATED TO COAL PROPERTIES

To help in assessing coalbed methane resources, methane adsorption cap acities of Permian coals from the Bowen Basin of Queensland were inves tigated and related to other coal properties. Maximum methane capaciti es of moisture-equilibrated coals, normalized to a pressure of 5 MPa a nd 30 degrees C, showed a continuously increasing (and reasonably line ar) trend with increasing rank over the range 80-92 wt% total carbon. Such a linear trend was not observed for methane adsorption calculated on a dry basis. Methane adsorption capacity decreased with increasing temperature by similar to 0.12 mL g(-1)K(-1). Methane capacity also d ecreased as moisture content increased, by similar to 4.2 mL g(-1) coa l for each 1 wt% increase in moisture. Coal surface area (CO2, Dubinin -Radushkevich) showed reasonable correspondence with methane capacity, although not precise enough to provide a reliable estimate of capacit y. Comparison of Langmuir adsorption isotherms for nitrogen and carbon dioxide on Bowen Basin coals with the corresponding methane isotherms showed that, with a knowledge of the methane isotherm alone, nitrogen and carbon dioxide isotherms could be reliably constructed. Volumetri c and gravimetric methane isotherms measured on the same coal were ide ntical, confirming the accuracy of the procedures and calculations use d. (C) 1997 Elsevier Science Ltd.