Partial Coal Pyrolysis and Its Implication To Enhance Coalbed Methane Recovery: A Simulation Study

A simulation study of partial coal pyrolysis to improve the petrophysics of coal seams and ultimately extract higher methane yields with accompanying pyrolysis gases was conducted, which was used to investigate the feasibility of partial coal pyrolysis for enhancing coalbed methane (CBM) recovery. Enhancing CBM production is an important subject for current CBM development, especially for low permeability coals. CBM exists mainly in an adsorption state in multiple micropores, which increases the complexity of CBM production. Pore volume and porosity in the low rank coal increased with increasing temperature. The permeability of the low rank coal increased exponentially with increasing temperature (300-400 degrees C) due to the generated pore fractures. The excessively high temperature of pyrolysis could result in the coals with the highest pore volume possessing the lowest methane adsorption capacity due to the extent of graphitization. Partial coal pyrolysis in a subsurface can increase the gas content, and improve the seepage ability of a CBM reservoir. CBM gas-in-place can be vastly increased (almost seven times the original CBM gas-in-place) by thermal treatment. The results indicated that the peak of daily gas production greatly increased and the gas yield peak arrived in advance for different rank coals with thermal treatment. By means of F.A.S.T. numerical software, gases in place and gas production for coal reservoirs after thermal treatment were acquired, which demonstrated that injected heat could promote CBM desorption, increase the coal permeability, and improve CBM production. Therefore, this technique may have significant implications for enhancing CBM recovery.