The Effect of Low Salinity Water on Wettability Alteration of Oil-Wet Calcite Surfaces

Abstract

To shed light on the chemical and physical aspects of low-salinity (LS) water flooding to enhance oil recovery, in this work, we explored the impact of the brine salinity on the interaction and modifications of the oil-calcite interface using a multi-technique surface science approach. FTIR, AFM, XPS, and Contact angle measurements were employed to characterize the adsorption and removal of commercial Nujol mineral oil on fresh cleaved single crystals of calcite CaCO3 (104) after conditioning into brines. Our results reveal that the initially oil-wetted calcite continuous film surface gives place to fragmented oil islands related to changes in the oil-calcite chemical interactions. More importantly, depending on the brine salinity, more oil was removed from the calcite surface, which is optimal for intermediate low-salinity water conditioning (LS75), as our semi-quantitative FTIR analysis demonstrated. Our laboratory scale model system has also shown considerable brine wettability alterations using LS75. A combination of AFM, FTIR, and XPS analysis suggests a competition between incorporating brine ionic species into the interface and the calcite dissolution. Interestingly, DW conditioning does not remove the largest portion of oil since dissolution can potentially increase the re-adsorption and anchoring of oil molecules, decreasing its overall removal.

Keywords: Enhanced oil recovery, wettability alteration, contact-angle, afm, XPS, FTIR