Experimental and Numerical Evaluation of CO2-Induced Wettability Alteration in Carbonate Reservoir CCUS

This study presents both laboratory measurements and numerical modeling of wettability alterations following carbon dioxide (CO2) injection in limestone carbonate reservoirs. Both synthetic and crude oil systems were evaluated using a Drop Shape Analyzer (DSA-100) to quantitatively measure the contact angle and interfacial tension (IFT) on limestone core samples under ambient and reservoir conditions. The results demonstrated that carbonated brine significantly reduced the IFT (2.0–4.1 dynes/cm) and contact angle (11.9–16.0°), indicating a shift toward more water-wet conditions, compared with the modest reductions in contact angle achieved with standard brine (1.6–6.7°). Synthetic fluid systems containing naphthenic acid initially exhibited stronger oil-wet behavior but also experienced wettability alterations when exposed to CO2. A previously developed compositional reservoir simulation model, which was based on assumed relative permeability endpoints, was revised to incorporate the experimental findings of this study as a supporting tool. Incorporating the experimental wettability alteration effect of CO2 in the numerical model by a 5.2% reduction in the residual oil saturation (the relative permeability endpoint) caused 2% increase in the oil recovery factor and 12% improvement in the CO2 utilization efficiency (9780 standard cubic feet per stock tank barrel (SCF/STB) vs. 8620 SCF/STB). Overall, this work provides critical laboratory validation and supports by numerical simulation that CO2-induced wettability alteration is a key mechanism underpinning CO2-based enhanced oil recovery (EOR) and carbon capture, utilization, and storage (CCUS) deployment in limestone carbonate formations.