CO[sub.2] Flow Characteristics in Macro-Scale Coal Sample: Effect of CO[sub.2] Injection Pressure and Buried Depth

Experimental studies have confirmed the permeability reduction of coal samples upon the adsorption of CO[sub.2]. However, these studies were carried out under limited experimental conditions. In this study, CO[sub.2] flow behaviors in a macro-scale coal sample were numerically simulated using a coupled gas flow, mechanical deformation, and sorption-induced deformation finite element model. The simulation results show that the effect of the reduction of effective stress on the enhancement of permeability is greater than the negative effect of permeability reduction due to CO[sub.2] adsorption for low injection pressures. CO[sub.2] pressure development in the sample increases with increasing injection pressure due to the enhanced advection flux for sub-critical CO[sub.2] injections, while for super-critical CO[sub.2] injections, CO[sub.2] pressure development, as well as concentrations in the sample, decreases compared to sub-critical CO[sub.2] injections because of greater density and viscosity of super-critical CO[sub.2] as well as coal matrix swelling induced by the adsorption of super-critical CO[sub.2]. Increasing axial stress (buried depth) obstructs CO[sub.2] migration in the sample due to the increased effective stress, and this effect is more influential for low injection pressures, which indicates that high CO[sub.2] injection pressures are preferred for CO[sub.2] sequestration in deep coal seams.