A variable-saturation pore electrical conductivity model for complex porous media saturated with supercritical carbon dioxide

Given the intricate nature of geological formations within supercritical carbon dioxide (scCO2) storage reservoirs, there is an urgent need to establish reliable models capable of monitoring changes in the scCO2 saturation. The variable-saturation pore electrical conductivity (VSPEC) model is proposed to monitor changes in the scCO2 saturation in sandstone accurately. The model considers pore geometry, roughness, capillary bundle expansion deformation, conductivity of carbonated water and multi-phase fluids distribution. The research finds that the VSPEC model accurately calculates the saturated pore radius and saturations of multiphase fluids. The specific surface resistivity of wall ion exchange becomes non-negligible when the water electrical conductivity is less than 1 × 10−3 S/m. The contribution of the carbonated water saturated to rock electrical conductivity reaches its maximum value as scCO2 saturation approaches 60 %. The effective carbonated water saturated radius ratio exhibits logarithmic growth in correlation with scCO2 saturation. Variations in the formation water salinity significantly impact both the electrical conductivity and solubility of scCO2. The VSPEC model can serve as a theoretical basis for field engineers to evaluate the effectiveness of scCO2 sequestration.