Effect of SO₄⁻² ion exchanges and initial water saturation on low salinity water flooding (LSWF) in the dolomite reservoir rocks

Abstract

The low salinity water injection has become one of the most important studies in the oil industry for improving oil recovery compared to conventional seawater injection. Thus, extensive studies have been conducted in carbonate and sandstone reservoirs to investigate how the physical properties of rocks and the chemical composition of fluids influence low salinity effect, while, the carbonate reservoir rocks requires more investigation of the effect of molecular and/or ionic interactions. In this experimental work, the effectiveness of various water flooding schemes in carbonate reservoir rock samples is investigated. In this regard, the oil recovery potential of seawater (SW), reservoir formation water (RFW) and managed water salinity (MWS), with different ion compositions adjusted based on the formation water composition are used. The experiments have been performed on the dolomite core samples and crude oil from an Iranian oil reservoir. Various measurements including zeta potential, XRD, contact angle and interfacial tension have been planned. The main contribution is to investigate the effect of both brine’s ionic composition and rock’s initial water saturation on wettability change and oil recovery. The results show that, the concentration of ${{\mathit{SO}}_4}^{-2}$ ion in the injected water must be managed over an optimum range for each case. This results in changing the wettability of carbonate rock to a less oil-wetting state by altering the brine composition and reducing the salinity. Moreover, initial water saturation plays a role in the process, so that, by increasing ${{\mathit{SO}}_4}^{-2}$ content in optimum range, the oil recovery increased.

Graphical Abstract

Keywords:

• Low salinity water injection
• EOR
• wettability alteration
• managed water salinity
• ${{\mathit{SO}}_4}^{-2}$ ion exchanges
• initial water saturation

Acknowledgments

Authors are very thanks from Iranian Offshore Oil Company (IOOC) and Abdal Industrial Project Management Company for supporting of the project. Also, they are grateful to Mr. Mohammad Rezaee, who is an EOR specialist in our research team for his technical and counseling support in laboratory.