Evaluation of CO₂ Storage Potential During CO₂ Mobility Control Optimization for Enhanced Oil Recovery

CO₂ mobility control by foam technology has enabled better sweep efficiency and, consequently, oil productivity during enhanced oil recovery (EOR) processes. Simultaneously with enhancing oil production, there is a sound potential for the in-situ generated foam to enhance CO₂ storage potential. However, the impact of the different in-situ foam generation strategies on the combined goal of maximum oil production and carbon storage is not well elucidated in the literature. In this study, we methodically evaluate the simultaneous optimization of CO₂ storage and oil recovery utilizing multiple injection strategies. Three flow experiments were performed in Indiana Limestone core samples deploying a zwitterionic surfactant as the foaming agent. In the first experiment, we investigated the use of pure supercritical CO₂ (scCO₂) on the oil production and the extent of CO₂ trapping in the used core, served as the base case. In the second and third experiment, we pre-flushed the porous media with a 0.5 wt% and 1 wt% surfactant solution slugs, respectively, followed by scCO₂ injection to evaluate the impact of a single-cycle surfactant alternating gas (SAG) injection strategy. Then, co-injection of the foaming agent and scCO₂ was attempted in both scenarios. The results show that the surfactant/scCO₂ co-injection method effectively controlled the mobility of scCO₂ by creating an advantageous environment and providing a continuous supply of surfactant solution for in-situ foam generation. Additionally, increasing surfactant concentration encouraged more effective mobility control due to the formation of higher stability foam and, consequently, improves the sweep efficiency and oil displacement process. In term of CO₂ storage, performing a single-cyle SAG led to an increase in the volume of CO₂ stored by 51% and 66% in the second and third experiments, respectively, relative to the base case. Based on the calculated volume element exchange parameter, it was noticed that the CO₂ storage effect during CO₂ flooding at 0.5 wt% and 1 wt% surfactant concentrations was relatively similar. On the other hand, by implementing the co-injection method, the higher surfactant concentration (1 wt%) results in better oil recovery but lower CO₂ storage potential compared to 0.5 wt%. The storage effect using 0.5 wt% surfactant solution was almost two times higher than the storage effect at 1 wt% concentration. We found that the higher foam strength due to increased surfactant concentration dominantly leads to more residual oil displacement than inducing more CO₂ storage. This finding ascertains that a thorough investigation of the injection strategy and composition is crucial before associating the CO₂ storage with CO₂ EOR or CO₂-foam EOR processes to achieve the most desirable ratio between stored CO₂ and oil recovery. Overall, the in-situ foam generation has proven to be beneficial to the dual purposes of carbon geo-storage and EOR.