Thermo-Mechanistic EOR Process Modelling in Deploying Low Salinity Hot Water Injection under Carbonate Reservoirs

Abstract

The potential of emerging low salinity water injection (LSWI) on heavy oil carbonate reservoirs has been reported with experimental studies. Wettability modification phenomenon by LSWI has been believed to be enhanced oil recovery. Temperature-dependent geochemical reactions including aqueous reactions, ion-exchange, and mineral dissolution contribute to the phenomenon. While LSWI has potential to recover residual oil, substantial oil has still been remained in reservoir due to high viscosity. Hot water injection is the economic enhanced oil recovery (EOR) method to produce heavy oil and has practical potential to deploy with LSWI. However, the temperature-dependent characteristics of geochemical reactions in LSWI mechanism requires to further evaluation of thermal energy effect when hybrid LSWI with hot water injection or hot LSWI, deploys.

In LSWI, kinetics of mineral dissolution has been accelerated by thermal energy to produce HCO3− and exchangeable Ca2+ into brine. Increased HCO3− reacts with H+ and produces CO2 (aq). The CO2 (aq) has transported into oil at thermodynamic equilibrium. Though this geochemical phenomenon has resulted in increased CO2 concentration in oil, the effect of viscosity reduction is negligible due to relatively low dissolved mineral concentration. The oil viscosity reduction obtained in hot LSWI is attributed to mainly temperature-dependent viscosity reduction, not geochemical contribution. However, another geochemical contribution is observed in terms of the produced Ca2+ from mineral dissolution. While the increased Ca2+ has been consumed to produce CaCO3, CaHCO3+, and CaSO4, it has contributed to enhancing ion-exchange in high temperature condition. This geochemical contribution has induced additional wettability modification over that from non-hot LSWI. Consequently, the enhanced ion-exchange and oil viscosity reduction by thermal energy significantly improve oil recovery in hot LSWI up to 7.8 % over LSWI.