Abstract:
In order to investigate the effect of temperature conditions on CO
2-ECBM (CO
2-enhanced coalbed methane), this study constructed a fully coupled model of CO
2-ECBM considering the non-isothermal adsorption effect based on the theories of adsorption thermodynamics and seepage mechanics, and systematically investigated the effect of different temperature conditions on the dynamic evolution of multi-physical fields in the CO
2-ECBM process. The results show that the desorption of CH
4 and adsorption of CO
2 in the CO
2-ECBM process are adsorptive and exothermic reactions, respectively, which will lead to significant changes in the temperature of the coal reservoir. With the extension of injection time, the coal reservoir temperature can be divided into four stages: slight decrease, sharp increase, sharp decrease and gradual stabilization, and the extension of injection time will lead to the gradual expansion of the temperature anomaly region in the coal reservoir. At the same time, the change of coal reservoir permeability is affected by the contraction/expansion of coal matrix due to gas desorption/adsorption and thermal expansion which compete with each other to determine the final evolution of coal reservoir permeability. In the area where CO
2 has not yet infiltrated into the coal reservoir, the contraction of the coal matrix due to CH
4 desorption dominates the evolution of the permeability of the coal reservoir, and the injection temperature is positively correlated with the permeability of the coal reservoir, while the initial temperature of the coal reservoir is negatively correlated with the permeability. After the intersection of CO
2 and CH
4 in the coal reservoir, the permeability of the coal reservoir is dominated by the net effect of gas competition adsorption and thermal expansion, and the relationship between the injection temperature and the permeability of the coal reservoir changes to a negative correlation, while the relationship between the initial temperature of the coal reservoir and the permeability changes to a positive correlation. In addition, the increase of injection temperature can effectively improve the CH
4 production efficiency and CO
2 storage efficiency, while the increase of initial temperature of coal reservoir can reduce the CH
4 production efficiency and CO
2 storage efficiency.