Thermodynamics, kinetics and modeling of sorption behaviour of coalbed methane – A review

The gradual depletion of the conventional energy reserves and ever growing energy demand has been the matter of global concern over the last few decades. Shrinking coal and petroleum resources have posed researchers to look for exploration and exploitation of unconventional gas resources. In this scenario, natural gas is not only a promising alternative solution towards mitigation of energy crisis but also a potential candidate to reduce the environmental impact through restraining the greenhouse gas effect. In this context, methane extraction from coalbeds has gained its commercial viability in different parts of the world viz. USA, China, Australia, India etc.

The review highlights global scenario of coalbed methane (CBM), transport of methane through coalbed, the sorption behavior of methane within the unconventional gas reservoirs, thermodynamic activities of gas adsorption into reservoir bed in terms of thermodynamics parameters viz. Gibbs free energy, temperature, enthalpy and entropy and the kinetic study of the contrivance of methane discharge for indicating the type of gas adsorbed onto the surface of coal matrix and time lapsed for saturation of coalbed. Maturity, geology and geochemical characteristics of coal have been reviewed for differential methane sorption in coal reservoirs. Diffusion and sorption isotherm model which fits the experimental data related to gas retention and release mechanism has also been discussed. Finally, different physicochemical characteristics of coal responsible for the methane gas storage and recovery have been discussed.