Experimental investigation on fluid/fluid and rock/fluid interactions in enhanced oil recovery by low salinity water flooding for carbonate reservoirs

[Display omitted] •Systematic investigation of Rock/Fluid and Fluid/Fluid interaction has been conducted.•Rock/Fluid and Fluid/Fluid interaction shows different optimum conditions for EOR.•Fluid/Fluid interaction is dominated by reduced IFT and increased viscoelasticity.•Rock/Fluid interaction is dominated by electrical double layer expansion and calcite dissolution.•Secondary and sequential flooding shows the dominance of Rock/Fluid interaction on oil recovery. The low salinity water flooding (LSWF) technique has established itself as cost-effective and environment-friendly in nature but its mechanisms are still unclear. Recovery due to LSWF mainly depends on two types of interaction, viz. fluid/fluid and rock/fluid. Despite the significant investigation, there is still no consensus on which interaction mainly governs oil recovery. This study intends to provide essential answers to the aforementioned issues, as well as additional significant insights into the dilution behaviour of Sea Water (SW) to be injected into a carbonate formation with equivalent salinity. A series of experiments were designed to assess both fluid/fluid and rock/fluid interaction thoroughly viz. compatibility test, IFT, interfacial rheology, zeta potential, and contact angle. A comprehensive number of individual and sequential coreflooding were conducted on outcrop cores to quantify the oil recovery potential of optimum salinities and gain more insight into wettability shifts due to LSWF. Rock/fluid and fluid/fluid interfaces showed different optimal conditions for improved oil recovery. Investigation of fluid/fluid interaction showed an optimal salinity of 2dSW as optimal salinity due to IFT reduction and increased viscoelastic properties. Rock/fluid interaction showed an optimal salinity of 10dSW due to enhanced zeta potential and calcite dissolution. Rock/fluid interaction showed an incremental recovery of 14% and fluid/fluid interaction showed an incremental recovery of 7% over simple SW injection. Sequential flooding based on rock/fluid interaction showed an incremental recovery of 16% over simple SW. Oil recovery based on rock/fluid interaction showed the highest recovery as compared to fluid/fluid interaction. Increased interfacial elasticity and calcite dissolution lead to wettability alteration and increased oil recovery due to LSWF. The effectiveness of LSWF depends upon optimum salinity and wettability alteration capability of low salinity slug. Results of this study also