Novel Approach to Enhance Organic Acid Adsorption on Rock Surfaces

Underground gas storage in depleted oil reservoirs has become an essential part of global energy demand since it has been proposed as a sustainable energy solution. The optimal storage of gases, especially hydrogen and carbon dioxide, requires an in-depth understanding of the rock-fluid interactions. Furthermore, the existence of different fluids within the reservoir rocks introduces complexity to the flow behavior, as the rock-fluid interaction can cause one fluid to oppose the flow of the other. The rock surfaces of depleted oil reservoirs contain adsorbed organic material as a result of fossil biodegradation, causing a change in the rock surface chemistry and thus a change in the rock-fluid interactions. Therefore, to simulate the anticipated contamination of geostorage rocks by organic molecules due to millions of years of exposure, a method to accelerate the adsorption of organic material on the rock surfaces is required. This work focuses exclusively on the adsorption of organic acids on quartz and calcite and seeks to optimize the adsorption process by a systematic study of the experimental conditions. The optimal experimental conditions that constitute the new method were found to be ionization over a 3 day period using a 1 M NaOH solution with a pH of 13. Based on our research results, it seems that the generation of the carboxylate ion (R-COO^-) at high pH values is more significant than the generation of a positive rock surface charge at low pH values. TOC, TOF-SIMS, and zeta (ζ) potential analyses were employed to validate the proposed method.