Numerical Study of the Influence of Well Spacing on the Production and Storage of CO2-ECBM

Abstract

The spacing between CO2 injection wells and CH4 production wells significantly influences the effectiveness of CO2-enhanced coal bed methane (ECBM) technology. Based on the theory of porous elasticity and seepage mechanics, a hydromechanical coupling model of CO2-ECBM was established, and the process of CO2-ECBM was simulated under varying CO2 injection pressures and well spacings, and the rules of CH4 production and CO2 storage under different well spacings were clarified. By constructing an objective function for evaluating the effect of CO2-ECBM project, the optimal well spacing corresponding to the four types of engineering targets under different injection pressures was obtained. The results show that reducing the well spacing can effectively enhance the effect of CH4 production and CO2 storage, but the enhancement effect weakens as the spacing is reduced, and the enhancement effect decreases or even disappears when the well spacing is less than 180 m. The optimal spacing for the four types of engineering targets increases with increasing injection pressure. Compared with the other three targets, although the engineering time under the time-saving and efficiency-enhancing target is significantly shorter, its corresponding CH4 production and CO2 storage effectiveness are markedly inferior. Therefore, it is believed that time saving and efficiency enhancing should not be regarded as a primary target in practical engineering. Finally, differentiated design strategies for CO2 injection pressure and well spacing are proposed under various engineering objectives, providing theoretical support for determining appropriate CO2 pressure and well spacing in the field.