The effect of low salinity water on wettability alteration of oil-wet calcite surfaces
Jesana M. Loreto, E. Annese, Ludiane Silva Lima, Lanna I.M. Sinimbu, Roberto F. S. Freitas, Guilherme Félix, Lucas G. Pedroni, andré Silva Pimentel, Fernando Stavale
Abstract
To shed light on the chemical and physical aspects of low-salinity (LS) water flooding to enhance oil recovery, we explored the impact of the brine salinity on the modifications of the oil-calcite interface using a multi-technique surface science approach based on FTIR, AFM , XPS , and Contact angle measurements. Our findings reveal that Nujol-model oil adsorbs on fresh-cleaved CaCO 3 (104) surface and initially forms a continuous film. Chemical and morphological surface characterizations were performed on oil-wet calcite , followed by their conditioning with formation (FW), demineralized (DW), and low salinity water (LS25, LS50, LS75, and LS100). The oil removal was quantified by semi-quantitative FTIR analysis and was found to vary from ∼20 % for FW up to ∼81 % for LS75 conditioning. In the investigated experimental conditions the fresh-cleaved calcite surface is most efficiently converted from oil-wet to water-wet when conditioned with LS75 brines. Significant surface wettability alterations were observed for LS 75 brines as contact angle measurements were found to reach a minimum contact angle of ∼18°. The changes in calcite wettability correspond to the formation of fragmented oil islands and calcite step bunches, the signature of surface dissolution, and changes in the oil-calcite chemical interactions. A model for Nujol adsorption and its detachment from the calcite surface was proposed for oil removal, competitive mechanisms related to the brine chemical composition are discussed.