Relationship between oil production and CO2 storage during low-salinity carbonate water injection in acid carbonate reservoirs

Abstract

This study investigates enhanced oil recovery (EOR) and CO2 storage efficiencies during low-salinity carbonate waterflooding (LSCWF) in carbonate reservoirs containing “acid” formation water. In order to identify the detailed geochemical reactions for acidic condition during LSCWF, simulational analysis was performed with “CMG-GEM”. After core-scaled model was constructed through history-matching processes based on the coreflooding experimental results, primary mechanisms during LSCWF were analyzed for various levels of injection water salinity. From the results of this study, CO2 dissolved in injected carbonate water yielded CaCO3 precipitation in acidic reservoirs, decreasing permeability significantly compared to in neutral reservoirs. In terms of wettability alteration and oil swelling by CO2 mass transfer, their effects were almost similar regardless of the salinity for both acid and neutral reservoirs. In the aspects of EOR and CO2 storage efficiencies, they strongly depend on the salinity for both acidic and neutral conditions. In the results of EOR–CO2 storage relationship, enhanced oil was smaller in acidic condition, while CO2 storage efficiency was not greatly related to acidity of the reservoir. The findings of this study can help for better understanding of smart water injection design into acid carbonate reservoir for the optimal EOR and CO2 storage efficiencies.