(389f) Effects of Wetability of Rock-CO2-Water System On the Migration and Distribution of Geologically Sequestered Supercritical CO2

CO2 sequestration (capture, separation, and long term storage) in various geologic media including depleted oil reservoirs, saline aquifers, and oceanic sediments is being considered as a possible solution to reduce green house gas emissions. Residual or capillary trapping is one of the most important mechanisms to impede the migration of supercritical (SC) CO2 and reduce leakage risks. The capillary pressure and relative permeability are key factors in sequestration, and they are strongly affected by the interfacial properties between SC CO2, saline and formation rocks. Interfacial properties are usually described by the interfacial tension and contact angle. A few experimental observations illustrate that the interfacial properties are functions of pressure, temperature, salinity and pH value of formation fluids, besides the mineralogy of formation rocks. The injection of SC CO2 can alter the in-situ conditions of P, T, pH etc. in target formations, and consequentially change the interfacial tension and contact angle. Preliminary analysis regarding the effects of wetability and entry pressure on the capacity and sealing efficiency have been presented. In this study, numerical simulations on idealized formations are conducted to investigate the effects of CO2 injection induced interfacial property alteration on the capillary pressure and relative permeability, and consequently on extent of migration and storage capacity. Simulations and analysts in this study are mainly concentrated on the effects of SC CO2 migration and its distribution for three properties: 1) reservoir rock formation wetability; 2) capillary pressure variation; and 3) variations in relative permeability. To date, experimental measurements reported have been focused mostly on the variation of interfacial tension and contact angle. Their effects are investigated in this research by scaling the capillary pressure calculated from the van Genuchten model with parameters estimated according from in-situ conditions (P, T, pH and salinity), using correlations presented by previous studies. By contrast, experimental investigations of the dependence of relative permeability on ??? are quite sparse in the literatures In order to facilitate our investigation, the modified Burdine model is adapted, in which the effects of contact angle are explicitly described. It is found that the SC phase irreducible saturation increases while the SC CO2 wetability of the reservoir formation rock is elevated, thus enhancing storage efficiency. By contrast, the sealing efficiency decreases caused by the reduction in the entry pressure threshold.