Numerical simulation of CO2 sequestration and enhanced coalbed mechane production cased by a pilot CO2-ECBM project in Qinshui basin, China
adsorption-thermo-hydro-mechanical-chemical(AHTMC) coupling, CO2 sequestration, coalbed methane, geochemical reaction, numerical simulation
Resource Development and Utilization > 6. Unconventional Natural Gas Geology and Development
Draft Paper Accepted
Xudong Liu / China University of Mining and Technology
Shuxun SANG / China University of Mining and Technology
Xiaozhi Zhou / China University of Mining and Technology
Ziliang Wang / China University of Mining and Technology
ABSTRACT: Injecting CO2 into the methane-bearing coal seams can not only store CO2 but improve coalbed methane recovery. In this paper a fully coupled adsorption-thermo-hydro-mechanical-chemical (AHTMC) model for CO2 enhanced coalbed methane (CO2-ECBM) is constructed, including the multiple fields with the coupling relationships of competitive adsorption of CO2 and CH4 in the coal matrix (A), gas-water two-phase flow in reservoir and gas diffusion in formation water(H), heat conduction/convection and energy changes caused by gas sorption, gas dissolution, geochemical reactions(T), coal deformation(M), geochemical reactions of various anions and cations and the mineral dissolution in formation water (C). The AHTMC model is verified by the cored coal sample experiments in the laboratory and applied to simulate a CO2-ECBM pilot project in Qinshui basin with different CO2 injection rates. Results show the CH4 adsorption capacity in the coal matrix decreases affected by CO2 competitive adsorption, and the hydrogen ion concentration in formation water increases after CO2 injection into the coal seam. With the increase of CO2 injection rate, the storage rate of CO2 decreases, the recovery rate of CH4 increases, and the pH value of produced water decreases significantly. The greater the distance between injection well and production well, the earlier CO2 breakthrough, the more notable the CH4 stimulation effect, and the earlier the pH value of produced water drops. The CO2 injection rate of 25 t/d can be applicable to the field project of CO2-ECBM because of the optimal CH4 recovery and CO2 sequestration, of which CH4 recovery increased by 14.89% compared with the primary and CO2 storage ratio is higher than 96% in a CO2 injection duration of 8000d.