Experimental investigation of smart carbonated water injection method in carbonates

Enhanced oil recovery (EOR) has been noticed during recent years from reservoirs that are at the end of their life plateau or in which production has been declined. Two of these EOR methods are as follows: carbonated water and smart water injection. In carbonated water injection method, CO2‐contained water is injected in reservoirs in order to decrease free CO2 injection mobility, increase water viscosity, and store/remove produced greenhouse CO2 gas safely, and in smart water injection method, the ions in brine are modified in order to make controlled reactions with distributed ions on the surface of rock to cause more hydrocarbon recovery. In this paper, the combination of these two methods is investigated as hybrid smart carbonated water injection to find out the recovery factor change and effective mechanisms. Experimental core flooding setup is used for investigation of hybrid EOR injection applicability and mechanisms. Probable mechanisms are measured using different cores and five water samples are used for preparing carbonated water (at pressure of 2500 psi) including sea water (34 261 ppm), river water (1329 ppm), one of Iranian reservoir formation water (FW) (163 711 ppm), 10 times diluted FW (0.1 FW), and 100 times diluted FW (0.01 FW). The effect of both brine content and volume of CO2 is determined during hybrid EOR assessment. The main mechanisms activated including pH variation, oil swelling, oil viscosity reduction, ion concentration variation in brine and porous media, and wettability alteration have been investigated. Hybrid method resulted in highest recovery (70%) mainly due to ion exchange, wettability alteration, oil swelling, and permeability enhancement. In addition, type of salt concentration will affect recovery as 0.01 FW results in 8% and 16% additional oil recovery compared to sea and river waters, respectively. Coupling of CO2 and salts will increase recovery factor due to mechanisms activated by each of these factors as 0.01 FW results in 10% more oil recovery compared to FW. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.