Simulation of key parameters in CO2 injection for enhanced coalbed methane recovery in a deep well group

Abstract

ABSTRACTThe use of CO2-ECBM technology in deep coalbeds, by taking advantage of high CO2 absorptivity, can displace more CH4 as well as keeping long-term sequestration of carbon dioxide in large quantities. Our experiments in the block of northern Shizhuang show that the coalbed has an adsorption capacity for CO2 which is two times of that for CH4. With the pressure dropping, CH4 (desorbs) more quickly than CO2, and can be displaced effectively. Changes in reservoir physical properties caused by CO2 injection mainly lie in permeability variations on account of matrix shrinkage and swelling during CO2 adsorption and desorption. Usually, the permeability declines at first and increases rapidly as the reservoir pressure drops. Based on such variation patterns, geological and numerical models are established to analyze the influence of volumes, frequencies and modes of CO2 injection on both methane production and recovery, as well as on CO2 burying potentials, of both the well group and single wells. The modeling result shows that the gas recovery increases after 2-year CO2 injection in the mode of 90-day injection, at a rate of 10–15 t/d, plus 90-day shut-in. Field tests indicate that the CO2 adsorption capacity of the No. 3 coalbed is 8 t/d while the burying potential of the whole well group is about 12616t.