Pore-confining pressure cycling test for supercritical CO2 permeability of sandstone: Implication for the nonlinear effective pressure law

The effective pressure law for the permeability of sandstone is experimentally studied by conducting Darcy's law permeability test under various confining pressure (from 14 to 58MPa) and pore pressure (from 8 to 23MPa). Supercritical CO2 as a pore fluid has been adopted instead of water for carbon capture and storage (CCS) study. The effective pressure law for permeability is associated with curved iso-permeability lines. We can express the effective pressure as P-eff = P-c - chi(P-c,P-p)P-p, where the coefficient chi corresponds to the slope of iso-permeability line according to the confining(P-c) and pore(P-p) pressure. It was confirmed that the coefficient is not a constant because of the nonlinearity of iso-permeability line. Cycling test of the permeability has been conducted for analyzing the phenomenon using a modified factorial method. The influence factor and interaction between the pore and confining pressure were analyzed.