Pressure Profiles Across Oil-Water Interfaces – A Molecular Modeling Study

Enhanced oil recovery (EOR) is an indispensible tool in the petroleum industry as it can recover substantially more oil than primary recovery. Typically, water or other substances are pumped into the reservoir to displace the oil in the rock. Understanding the interface between crude oil and water (or its vapor) is clearly crucial to understand such techniques. For example it is known that the surface tension of crude oil scales close to linear with density but the surface tension values are significantly smaller than those for alkanes of the same density. This is presumably due to preferential accumulation of light end alkanes at the crude oil surface.  

 We perform atomistic simulations of alkanes and aromatics as model crude in contact with water. The density profiles show an enhancement of aromatics at the interface. We then determine for the first time detailed pressure profiles across the crude oil-water interface and determine surface tensions in several independent manners. We find that the interfacial structure breaks the symmetry as revealed by the differences in pressure profiles on the water and the oil side of the interface.