Experimental study of microscopic oil production and CO2 storage in low-permeable reservoirs

Enhanced CO 2 sequestration (ECS) within low-permeable reservoirs during CO 2 -enhanced oil recovery (CO 2 -EOR) processes has gained significant interest, primarily driven by the need to mitigate the greenhouse effect caused by excessive CO 2 emissions. In this work, the in-situ nuclear magnetic resonance (NMR) is applied to investigate the oil production and CO 2 sequestration within the micropores of low-permeable reservoirs. Additionally, the impact of CO 2 –water–oil–rock reactions on CO 2 -EOR and CO 2 sequestration is studied by analysis of the changes in minerals, pore structures, and wettability of cores by scanning electron microscopy (SEM), X-ray diffraction (XRD), and contact angle measurements with the experiments of CO 2 –water–oil–rock interaction in the high-temperature and high-pressure (HT-HP) reactor. The results reveal that the residual water saturation ( S wr ), CO 2 injection pressure, and the interaction among CO 2 , water, oil, and rock all exerted a considerable impact on oil recovery and CO 2 sequestration. Compared with the oil recovery and CO 2 sequestration of the two oil-saturated cores (Core No. 2 and Core No. 3) after CO 2 injection, the accumulated oil recoveries of the two cores with S wr = 0.5 are enhanced by 1.8% and 4.2%, and the CO 2 sequestration ratios are increased by 3% and 10%, respectively. Compared with the CO 2 –water–rock that occurred in oil-saturated cores, the CO 2 –water–rock reaction for cores ( S wr = 0.5) is more intense, which leads to the formation of more hydrophilic rock on pore surfaces after the reaction, thereby reducing the adhesion work of CO 2 stripping oil. The oil and water mixtures in pores also inhibit CO 2 premature breakthrough from cores, therefore expanding the swept volume of CO 2 in cores. Otherwise, oil recovery and CO 2 sequestration in small pores of cores are significantly improved with the rise in CO 2 injection pressure due to the enhanced driving pressure degree and also the improved mutual solubility and mass transfer between CO 2 and oil.