Gas reservoir simulation for enhanced gas recovery with nitrogen injection in low permeability coal seams

Gas drainage is an integrated strategy in mining gassy seams to establish a safe mining environment. A range of properties and operational conditions affect the performance of enhanced gas drainage process using a stimulating gas. The micro-structures of a coal sample from an Australian gassy coal mine were analysed using field emission scanning electron microscopy (FESEM). Results show that the micro-fissures between the matrixes are extremely narrow and tight thus contributing to hard-to-drain problems. A gas reservoir simulator was used to investigate the key parameters in gas drainage processes involving the injection of nitrogen. Simulation results show that methane content was reduced from 11.9 m(3)/t to less than 6.6 m(3)/t, and the methane recovery rate was greater than 78% within a gas drainage lead time of 180 days. The paper concluded that enhanced gas drainage with nitrogen injection is a promising strategy for extracting methane from low permeability gas reservoirs.