Influence of Carbonated Water on CO₂ Residual Trapping in Berea Sandstones

The storage of captured CO₂ in deep geological formations has been the most commonly used practice in the industry for the disposal of anthropogenic gas from the atmosphere. The formation into which the CO₂ is stored has a wetting phase, which can be either water for saline aquifers or oil in the case of depleted reservoirs. Previous studies have explored the alteration of wettability that occurs as a result of the interaction of CO₂ with sandstone rock surfaces over a short duration of exposure time. This study, however, aims to understand the effect of prolonged CO₂ interaction with Berea sandstone rocks on the wettability of saline aquifers and depleted oil reservoirs during CO₂ sequestration. In this work, carbonated brine consisting of 3 wt % NaCl brine and CO₂ was formulated and exposed to Berea sandstone samples with a quartz content of >97% with different wettabilities (water-wet and oil-wet samples). The oil-wet samples were made by treating geologically similar Berea sandstone samples with a solution consisting of 2 wt % oleic acid in ethanol. The water-wet and oil-wet samples were exposed to the formulated carbonated brine for a duration of 30 days at 75 °C and 1800 psi. Capillary pressure curves were generated using the porous plate method to investigate the wettability evolution of both water-wet and oil-wet samples prior to and after exposure to carbonated brine. The results from the aging study revealed that carbonated brine can make a rock surface hydrophilic due to the interaction of acidic brine with the rock surface or by removing organic materials from the rock surface. The results also showed that the oil-wet samples became more hydrophilic (by up to 66%) compared to the water-wet samples (59%). The increase in the hydrophilic behavior of both water-wet and oil-wet samples thus leads to higher residual trapping. This study concluded that the residual trapping of sandstone saline aquifers and depleted oil reservoirs can be influenced by the continuous interaction of scCO₂ with the rock surface.