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

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.

Automated summary

Low salinity water flooding is a novel enhanced oil recovery method that has gained attention in recent years. Optimization of the composition of injection water is crucial to reduce the risk of incompatibility and formation damage. This study presents a detailed workflow to maximize wettability alteration and minimize compatibility in a core model of carbonate rock using a genetic algorithm. The results indicate that there is no unique optimized water composition for an efficient low salinity water flooding process, and suggestions for optimization are provided.