Effect of Pore and Confining Pressure on the Supercritical CO₂ Permeability: Implications for the Effective Pressure Law

The aspect of the change in the liquid permeability of rock using distilled water and brine has been reported to be different from that of using gas according to confining pressure P_c and pore pressure Pp. In this study, as part of the research on CO₂ geological storage, the permeability of sandstone was measured using supercritical CO₂ which has gas and liquid properties simultaneously, and the effect of P_c and P_p on this permeability was analyzed. For supercritical CO₂ to be utilized, the series of non- Darcy flow tests with high flow rate were conducted, and the permeability was estimated through the Forchheimer equation considering an inertial flow. An effective pressure coefficient for permeability was derived experimentally to be applied to the effective pressure law. First, we investigated pressure conditions with identical permeability for plotting the iso-permeability line. From the effective pressure law, the effective pressure coefficient of permeability corresponds to the slope of the iso-permeability line. As a results, upon the confining or pore pressure conditions, varied permeability and effective pressure coefficient indicated. To clarify the variation of the coefficient depending on the pressure conditions, we attempted to drive a second-order effective pressure coefficient for which the interaction between P_c and P_p was considered. The coefficient increased non-linearly as the difference of P_c and P_p decreased, with a maximum of 1.36 being observed. The validity and correlation between the effective pressure with the coefficient and the permeability were examined by applying empirical models of permeability dependent on effective pressure.