Sorption Isotherm for Coalbed Methane Exploration - A Case Study from Jharia Coal Basin, Bihar, India

Methane produced from coal seam is going to be an increasingly important commercial resource in the Jharia Coalfield of India. However, coal seams in general are poorly understood with respect to their behaviour as gas reservoirs. Gas is predominantly stored in an adsorbed state, as opposed to a compressed state. For the exploration and assessment of coal bed methane, it is important to understand the mechanism of adsorption, retention and accumulation of methane gas within coal seams during the process of coalification. A laboratory investigation into the sorption characteristics of a coal seam from Jharia basin led to the generation of an adsorption isotherm. The Langmuir adsorption isotherm defines the relationship between the capacity of coal to store gas to the external pressure of the gas. At low pressure, the relationship between storage capacity and pressure is linear and is referred to as Henry’s Law isotherm. Sorption provides a predictive information into “Gas Storage Capacity” and “Recovery Factor”.