A Comprehensive Experimental Study of Pore-Scale and Core-Scale Processes During Carbonated Water Injection Under Reservoir Conditions

Abstract Enriching the injection water with CO2 has demonstrated promising results as a method for improving oil recoveries and securely storing CO2 in oil reservoirs. However, the mutual interactions taking place between carbonated water and reservoir oil at elevated reservoir conditions are not fully understood. Here we present the results of a thorough investigation of the processes leading to additional oil recovery through integrating pore-scale visualisations and coreflood experiments. Four pore-scale visualization (micromodel) experiments were performed at reservoir conditions using the recombined live oil under different injection scenarios (tertiary and secondary). Having identified the underlying dynamic interactions at pore-scales, the performance of different injection scenarios for carbonated water injection (CWI) was investigated using carbonate reservoir rocks. Five coreflood experiments were carried out using both fully and half-saturated carbonated water to sensitise the impact of CO2 content of injection water on the performance of CWI. In-situ liberation of gaseous phase was identified (from direct visualisations) as the predominant mechanism controlling the performance of carbonated water injection. The gas phase formation would bring about higher degrees of oil swelling, and it would also create a three phase flow regime which leads to further reduction of residual oil saturation. The observations confirm that the performance of CWI should be investigated under reservoir conditions using multi-components live oil and reservoir cores. Any simplification, e.g. one components make-up gas or reduced pressure/temperature, of the reservoir conditions would misleadingly change the pore-scale event and hence, the performance of CWI. From the core displacement tests, it was observed that secondary CWI could recover a significant amount of additional oil, which was 26% compared to plain seawater injection. The tertiary carbonated water would effectively mobilise 15.3% of the residual oil (after seawater injection). When CO2 content of injected CW (carbonated water) was halved, the oil recovery dropped by 13. The results revealed that the oil recovery would be lower if CO2 concentration is reduced but the extent of oil recovery reduction would be much less than the level of reduction in CO2 concentration. The unique and integrated research approach employed here enables us to produce a more complete and reliable set of findings and understandings at realistic reservoir conditions. During CWI under reservoir conditions, an "in-situ WAG-type" three-phase flow would be generated with more effective sweep efficiency and pore-scale advantages.