A Review and Evaluation of Laboratory-to-Field Approach for Low-Salinity Waterflooding Process for Carbonate Reservoirs

Low-salinity waterflooding (LSWF) process has gained much attention in recent years as a promising enhanced oil recovery (EOR) method because of its potential for a superior performance, especially through extensive laboratory studies. This study reviews a rigorous and systematic laboratory-to-field approach involving research, discovery and validation using experimental and simulation components. The impact of various ionic compositions on LSWF is evaluated including a fundamental understanding of water geochemistry and the likely geochemical reactions that would occur during the process. Roles of crude oil/brine/rock (COBR) interactions and resulting rock surface charges are investigated as well. In so doing, authors present findings of their studies to support their analysis. Both experimental and simulation components are treated as complementary to each other. Experimental components included reservoir-condition high-pressure high-temperature (HPHT) displacement tests in composite cores using brines of different salinities and specially designed ionic compositions; investigation of wettability alteration—presumably a key LSWF mechanism—in a unique and specifically designed HPHT imbibition cell; Zeta potentiometric studies using a Zeta potentiometer capable of more representative evaluation in brine-saturated whole cores rather than with pulverized samples. Simulation studies involved validation of likely geochemical reactions during LSWF; incorporating oil/brine/rock interactions, and then, linking laboratory data to data from a candidate reservoir to complement the process. Findings of the coreflooding experiments proved conclusively that LSWF with certain specific ionic composition yielded a higher oil recovery. HPHT imbibition tests yielded both visual and quantitative estimations and visual real-time monitoring of how the wettability alteration took place during LSWF and how it was impacted by the degree and magnitude of both temperature and pressure as the vivid variations in the contact angles were clearly captured. Using a whole reservoir core rather than pulverized samples, Zeta potentiometric studies enabled an investigation of the charging behavior at the rock-water interface at various salinities. A new method to estimate Zeta potential in high-salinity environment was developed and validated, and it conclusively proved that rock surface charge played a vital in the LSWF process. The simulation studies included incorporation of experimental