Analysis of the Impact of CO₂ Adsorption on Rock Wettability for Geological Storage of CO₂

Abstract

Wettability change of rocks under high-pressure CO 2 is analyzed for CO 2 storage assessment. Increased water contact angle (measured by the sessile drop method) with CO 2 pressure on three different rocks is related to CO 2 adsorption on the rocks using complementary experimental results of CO 2 adsorption (by gravimetric measurement) and interfacial tension between water and CO 2 (by the pendant drop method). An analysis of free energy change accompanying CO 2 adsorption on the rock surface shows that adsorbed CO 2 could result in moving the CO 2 /water/rock contact line and change the rocks from water-wet to non-water-wet, increasing the potential for CO 2 to spread and displace water. The free energy change has not been studied previously, and the results suggest that CO 2 adsorption on rocks could decrease the capillary force in geological reservoirs and enable injected CO 2 to enter a greater portion of pore space. This would significantly increase the reservoir utilization efficiency and CO 2 storage capacity.