Abstract
This paper resolve the salinity-dependent interactions of polar components of crude oil at calcite-brine interface in atomic resolution. Molecular dynamics simulations carried out on the present study showed that ordered water monolayers develop immediate to a calcite substrate in contact with a saline solution. Carboxylic compounds, herein represented by benzoic acid (BA), penetrate into those hydration layers and directly linking to the calcite surface. Through a mechanism termed screening effect, development of hydrogen bonding between –COOH functional groups of BA and carbonate groups is inhibited by formation of a positively-charged Na+ layer over CaCO3 surface. Contrary to the common perception, a sodium-depleted solution potentially intensifies surface adsorption of polar hydrocarbons onto carbonate substrates; thus, shifting wetting characteristic to hydrophobic condition. In the context of enhanced oil recovery, an ion-engineered waterflooding would be more effective than injecting a solely diluted saltwater.
Highlights
This paper resolve the salinity-dependent interactions of polar components of crude oil at calcitebrine interface in atomic resolution
We performed molecular dynamics simulations to explore the affinity of a polar aromatic hydrocarbon to preferentially adsorb onto calcite mineral in NaCl brines of different salinities
Despite a persisting water monolayer, benzoic acid (BA) directly adsorbs onto calcite via its –COOH functional group by developing hydrogen bonding with O-atoms of surface carbonate groups
Summary
This paper resolve the salinity-dependent interactions of polar components of crude oil at calcitebrine interface in atomic resolution. Wetting state of naturally occurring minerals, termed as wettability, is an ion-specific property, which could be effectively modified via manipulating ionic content of surrounding brine solutions[9,10,11] This virtue is central to an operation in the oil industry for enhanced oil recovery (EOR), mostly using water with different salinities. The injection of low salinity brine into the reservoirs disturbs the long standing thermodynamic equilibrium at mineral/formation water interface[20] Such disturbances complicate the governing mechanisms of oil/brine/ rock interactions and is the reason behind the uncertainties dealing with LSW14,17,21. It is natural to expect different salinity response for the interaction of carboxylic acids with calcite compared to ionized molecules It seems that the complexity of crude oil is partly the origin of inconsistent observations obtained in experiments concerning brine. Some of the impacts of ions include ion-exchange[37,40], pinning point[41] and screening e ffect[42] which diversely alter rock wettability
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