A Lab-to-Field Approach and Evaluation of Low-Salinity Waterflooding Process for High-Temperature High-Pressure Carbonate Reservoirs

Abstract

Abstract Low-salinity waterflooding (LSWF) process has gained great attention over the years as a promising enhanced oil recovery (EOR) method with its superior performance over high-salinity water waterflooding. This study presents a rigorous and systematic lab-to-field approach involving research, discovery and validation using experimental and simulation components. Impact of various ionic compositions on LSWF was determined including a fundamental understanding of water geochemistry and likely geochemical reactions. The roles of crude oil/brine/rock (COBR) interactions and resulting rock-surface charges were investigated as well. Both experimental and simulation components were 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 were conducted using a Zeta potentiometer capable of more representative evaluation in brine-saturated whole cores rather than with pulverized samples. Simulation involved: proposing likely geochemical reactions during LSWF; incorporating oil/brine/rock interactions, and then, simulation studies linking laboratory data to data from the candidate reservoir on complementary basis. The findings of the coreflooding experiments proved conclusively that LSWF with certain specific ionic composition yield a higher oil recovery. HPHT imbibition tests yielded both visual and quantitative estimations and 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, if not a more dominant role, in the LSWF process. The simulation studies included incorporation of experimental data generated during the study, identification of a set of likely geochemical reactions during the process and complementary field data to study the LSWF performance under various conditions and constraints. A conceptual "lab-to-field" approach that can contribute to designing a more efficient LSWF process with optimized ionic chemistry has been proposed based on results and analysis from this study.