Mechanism of wettability alteration of the calcite {101[combining macron]4} 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 Mg(2+)and Ca(2+)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.