Simulation Study on the Behaviour of N2 and CO2 Injection and Their Mixtures on ECBM Recovery

The challenge to produce hydrocarbon from conventional type of reservoirs are getting tougher and tougher. Therefore, there is a need to look into alternatives source of method which is by means of looking into the prospect of unconventional reservoir- production of coalbed methane. There are few differences between conventional and unconventional reservoirs. In conventional reservoir, hydrocarbon is produced first while water acting as an aquifer support will be produced later once the hydrocarbon is depleted. Meanwhile, in unconventional reservoir, water is produced first to depressurize the water pressure (hydrostatic pressure) that is acting on the coal seam so that methane (CH4) gas is allowed to escape from the coal matrix. Deep coal is able to hold considerable amount of gas but due to different type of coal ranks and high lithostatic load on the coal resulting in very low permeability makes producing gas from such reservoir a challenge. Enhanced Coalbed Methane (ECBM) recovery process is a type of method to improve the recovery process of methane gas after the primary production is declining. One of the method mostly used are the injection of gas to replace the methane gas in the pore matrix. The behavior of injected gases; CO2 and N2 alone and their mixtures will be simulated into 2 commercial and one non-commercial fields (San Juan Basin, Powder River Basin, and Balingian Coalfield) will be analyzed and compared. The simulation process will be conducted by using popular and easily available simulators like ECLIPSE simulator. Based on the simulation results, fields that are simulated by injection of pure nitrogen gas yield the highest amount of total recovered methane (CH4) gas.