Construction of high-pressure adsorption isotherm: A tool for predicting coalbed methane recovery from Jharia coalfield, India

Adsorption isotherm relates the gas storage capacity as a function of pressure at constant temperature. In this paper, adsorption isotherm of two dry borehole samples was constructed in the laboratory using the manometric method. Isotherm was measured for two gases, i.e., CH4and CO2to pressure up to 8.4 MPa. Before the construction of sorption isotherm, coal was characterized by proximate, ultimate and petrographic analysis. Coalbed gas content of these two samples was found 2.29 m3/t and 2.75 m3/t. SEM images were obtained for the pore size distribution of coal using pore image analysis. Prediction of coalbed methane recovery from CH4adsorption isotherm showed that these coalbeds are under saturated. CO2isotherm was constructed to estimate enhanced coalbed methane (ECBM) recovery. Volume wise CO2/CH4sorption ratio was found 2.09 times to 2.75 times respectively. This paper presents the interpretation of isotherm data to find the recovery factor of methane production from Jharia coalfield.