The impact of monovalent and divalent ions on wettability alteration in oil/low salinity brine/limestone systems

Abstract

Waterflooding is applied worldwide to improve oil recovery. Due to the complexity of the crude oil-brine-rock interactions, the mechanism behind the low saline enhanced oil recovery (EOR) process has been debated in the literature for the last decade. Both physical and chemical mechanisms have been proposed, but it appears that none of the suggested mechanisms have got a general acceptance in the scientific literature so far. The main objective of this paper is to investigate the affinity of ions toward the surface during low and high salinity injection by measuring the contact angle (CA) and interfacial tension (IFT) in a carbonate rock substrate/oil/brine system, in different salinity and pH levels. The brines were original sea and formation water, brine solutions containing single component salt such as; MgSO4, KCl, Na2SO4, CaCl2, MgCl2, NaCl, and multicomponent mixtures of them at different concentrations. Three different stock-tank crude oils are utilized in this study. Results showed that the asphaltenic-acidic crude oils have a positive impact to wettability alteration of carbonate rocks during low salinity water injection. Also we observed that the low salinity waterflooding possibly behaving similar to alkaline flooding due to increase in pH. The IFT results show that the lowest IFT value is obtained at 5000ppm smart water containing divalent ions, Mg2+ and SO42−.