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

Wettability change of rocks under high-pressure CO2 is analyzed for CO2 storage assessment. Increased water contact angle (measured by the sessile drop method) with CO2 pressure on three different rocks is related to CO2 adsorption on the rocks using complementary experimental results of CO2 adsorption (by gravimetric measurement) and interfacial tension between water and CO2 (by the pendant drop method). An analysis of free energy change accompanying CO2 adsorption on the rock surface shows that adsorbed CO2 could result in moving the CO2/water/rock contact line and change the rocks from water-wet to non-water-wet, increasing the potential for CO2 to spread and displace water. The free energy change has not been studied previously, and the results suggest that CO2 adsorption on rocks could decrease the capillary force in geological reservoirs and enable injected CO2 to enter a greater portion of pore space. This would significantly increase the reservoir utilization efficiency and CO2 storage capacity.