Interpreting Screening of Appropriate Carbonate Reservoir for Low Salinity Water Flood EOR in Giant Indian Offshore Fields

Abstract

Abstract In offshore giant carbonate reservoirs low pressure, high salinity, and high temperature make popular liquid-based EOR a challenge. But tuning injection water salinity/ ionic composition can increase both microscopic and macroscopic displacement efficiency in carbonates screened based on temperature, wettability, and potential determining ions (PDI). The study includes an analysis of major offshore fields of India and highlights key factors that showed a positive impact of low salinity water flood (LSWF). The main emphasis of this paper is on 1- Screening of carbonate reservoir offshore fields based on spontaneous imbibition and wettability index experiment; 2- Core flood displacement experiment for proper evaluation of LSWF effect based on incremental recovery; 3- Optimization of salinity on carbonate core samples in both tertiary and secondary mode water flood; 4- Relative permeability curve generation for both high salinity seawater (HSSW) and Optimized low salinity water (OLSWF) water through single porosity core model simulation based on laboratory experiment inputs and 5- Pilot area simulation to quantify the benefit of OLSWF on a field scale. The main conclusions of the study are 1- Wettability index and spontaneous imbibition (SI) experiments indicate a potential low salinity effect; the presence of clays, formation, and injection brine composition, presence of potential determining ions determines the impact of oil recovery for screening of fields; 2- Displacement studies indicated an incremental recovery of (5.6-15.9% HCPV) respectively over seawater flooding owing to a reduction of salinity; 3- Salinity optimization study reduce the potential risk of incompatibility between injection water and the initial crude-oil/brine/rock system. Rock-fluid compatibility studies confirm 25% seawater (SW) salinity as optimum salinity with maximum incremental recovery with diluted versions of seawater having a salinity range from 33640 ppm to 336 ppm; 4- Relative permeability curve generated for both high salinity seawater (HSSW) and optimized low salinity water (OLSWF) water with the help of 1D Core flood simulation. The oil recovery profile was used to generate a reasonable match between experimental and simulation results. Residual oil saturation decreases by about 10 saturation units under low salinity flooding in imbibition mode; 5-Simulation Study envisages incremental oil gain of 1.37 MMt over the base case with incremental oil recovery of 1.5%. The originality of the paper lies in the finding of the potential of LSWF for offshore carbonate reservoirs at high-temperature ranges along with its confirmation by a shift in the relative permeability curves through the wettability alteration phenomenon. The positive outcomes serve as guidelines for carbonate reservoir screening and the science of rock fluid interactions at the pore scale in LSWF.