Evaluation of CO2 Storage Potential During CO2 Mobility Control Optimization for Enhanced Oil Recovery
Authors: Hanamertani Alvinda Sri , Yu Ying , Elkhatib Omar , Ahmed Shehzad , Jiao Zunsheng , McLaughlin Jonathan Fred 
Published: May 2023

Abstract
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.