Optimization of injection water composition during low salinity water flooding in carbonate rocks: A numerical simulation study

Abstract

Low salinity water flooding as a novel enhanced oil recovery method has gained increased attention especially during the past decade. Akin to other methods, low salinity water flooding carries some risks, being able to lead to failure in the target reservoir. To reduce the potential risk of incompatibility between injection water and initial crude-oil/brine/rock system, the composition of injection water needs to be optimized to prevent formation damage due to incompatibility problem. Moreover, careful selection of injection water composition would profoundly influence the performance of low salinity water flooding. In this study, a detailed workflow is presented to resolve problems in terms of maximizing wettability alteration and minimizing compatibility in a core model of carbonate rock. The proposed framework can be utilized to plan an effective low salinity water flooding injection. For simulation of low salinity water flooding, the method proposed in our previous work considering time-dependent wettability alteration was applied. Furthermore, genetic algorithm (GA) was utilized to optimize injection water composition. In the proposed method, a geochemical software (PHREEQC) was coupled with GA optimizer and a commercial numerical simulator. Prior to any numerical simulation, for each suggested scenario by GA, compatibility between injection and formation water was examined via mixing in this geochemical software and evaluation of saturation index. Results demonstrated that no unique optimized water composition can be advised for an efficient low salinity water flooding process. Furthermore, some suggestions are put forward for optimization of low salinity water flooding. • Presenting a detailed workflow to maximize wettability alteration and to minimize compatibility problems during LSWF. • Applying time-dependent wettability alteration for LSWF in a core model of carbonate rock. • Coupling of PHREEQC, ECLIPSE and GA to find the optimal ions concentration. • Utilizing saturation index for compatibility check of injection water with formation water to prevent undesired scenarios.