Evaluating CO₂ Residuals in Water Aquifers and Depleted Oil Reservoirs via X-ray Core-Flooding Experiments

The success of carbon dioxide storage depends on the security of the stored gas from leakage to the surface. This security is ensured when there is an interaction between CO₂ with the formation water and the surrounding rock to trap it in other forms. The formation into which CO₂ is stored has a wetting phase, which can either be water-wet for the saline aquifer or oil-wet in the case of the depleted oil reservoir. Therefore, this study aims to enhance the understanding of the CO₂ flow behavior in Berea sandstone rocks and determine the role that the interaction between the fluids and the solid plays on the wettability of rocks during CO₂ storage. In this work, a series of CO₂ core-flooding experiments were performed on Berea sandstone core samples with a quartz content of >90%. The wetting nature of the sample was altered by treating it with 2 wt % oleic acid to mimic a depleted oil reservoir. The X-ray scanning technique was applied to detect the CO₂ saturation and CO₂ residual after the core-flooding experiments. The results from the core-flooding experiments revealed that the oil-wet sample has higher CO₂ residual trapping (43.2%) due to the high interaction and adsorption between CO₂ and the organic surface.