Carbonated Smart Water Injection for Enhanced Oil Recovery in Sandstone Reservoirs of Upper Assam Basin, India

Abstract

Smart water injection (SWI) and carbonate water injection (CWI) have been successfully used in enhanced oil recovery (EOR) due to favorable crude oil-brine-rock interactions. In this study, these two EOR methods are combined as one hybrid EOR process namely carbonated smart water injection (CSWI). An attempt was made to study the EOR potential in sandstone reservoirs of Upper Assam Basin in India. The synergetic effects in CSIR arises due to analogy between CO2 solubility in brine and composition/concentration of brine. First, characterization of reservoir rock and fluids collected from major producing oilfields of Upper Assam Basin. Second, optimal smart water for the candidate reservoirs determined by measuring the contact angles and oil-water IFT at different compositions and concentrations of formation water. Third, preparation of carbonated smart water and effect on reservoir rock wettability. Fourth, screening optimal carbonated smart water solutions. Fifth, applicability of the CSWI method as an EOR technique in sandstone reservoirs investigated using lab-scale core flooding experiments and the results compared with the oil recovery by SWI and CWI methods. The analyses also marked the crude as medium gravity, acidic and suitable for alkaline flooding. The formation water analysis showed the presence of different types of dissolved cations and anions with total salinity of 9534 ppm. From the original oil-wet (ϴ = 115°) state of the core, wettability alteration to intermediate-wet (ϴ = 79°) conditions were achieved with smart water. The IFT experiments demonstrated the EOR potential of smart water as the oil-water was reduced by more than half from the initial 22.18 to 7.59 mN/m. The use of carbonated water on the core surface changed core wettability to a water-wet because there was a reduction in the pH of the aqueous phase, and this modified the charges on the oil/water, and water/rock interfaces, and hence the wettability of the system. Optimal CSWI formulations screened based on contact angle and IFT measurements were used for tertiary flooding resulted in incremental oil recovery of approximately 14.44 % oil in place. This recovery was sufficiently higher than the HSB and LSB flood recoveries of 35.98% and 45.38% respectively. Thus, the core flooding highlighted the EOR potential of CSWI in sandstone reservoirs. The combined CSWI process when applied to sandstone reservoirs increases the efficiency of wettability alteration due to the ability of carbonated smart water to modify the crude oil-brine-rock interactions. Thus, both CWI and SWI can be effectively combined and engineered to achieve improved oil recovery in sandstone reservoirs. Moreover, during CSWI processCO2 moves from the brine into the oil phase, which altered the reservoir rock characteristics and the physical properties of reservoir fluids.