An analysis of the effect of CO2 injection on the recovery of in situ methane from bituminous coal: an experimental simulation

A set of experiments is described in which CO/sub 2/ is injected into large cores of CH/sub 4//sup -/ and water-saturated bituminous coal at elevated pressures. CO/sub 2/ at pressures up to 800 psig (5516 KPa) is used to simulate the enhanced recovery of in-situ CH/sub 4/ from coal beds. CO/sub 2/ injection increases the recovery of CH/sub 4/ by a factor of two to three times that achieved in simple desorption by pressure drawdown and atmospheric diffusion. In general, higher CO/sub 2/ pressures achieve greater CH/sub 4/ recovery. The presence of even small amounts of N/sub 2/ in the injection gas greatly reduces the CH/sub 4/ recovered. CO/sub 2/ at 500 to 800 psig (3447 to 5516 kPa) is shown to be capable of completely demethanating integral coal samples. This was confirmed by tests run on crushed cores. CO/sub 2/ consumption by permanent adsorption is quite high vis-a-vis the CH/sub 4/ recovered and may preclude its use as an enhanced-recovery energy process. Its primary function would appear to be as a means of safely demethanating coal beds before mining.