Mechanism of wettability alteration of the calcite {1014} surface

To understand the mechanism of wettability alteration of calcite, a typical mineral in oil reservoirs, the interactions of deionized water and brine (with different compositions) with the calcite {1014} surface are investigated using a combination of molecular dynamics and first-principles simulations. We show that two distinct water adsorption layers are formed through hydrogen bonding and electrostatic interactions with the calcite {1014} surface as well as hydrogen bonding between the water molecules. These highly ordered water layers resist penetration of large stable Mg2+ and Ca2+ hydrates. As Na+ and Cl- hydrates are less stable, Na+ and Cl- ions may penetrate the ordered water layers to interact with the calcite {1014} surface. In contact with this surface, Na+ interacts significantly with water molecules, which increases the water-calcite interaction (wettability of calcite), in contrast to Cl-. We propose that formation of Na+ hydrates plays an important role in the wettability alteration of the calcite {1014} surface.