First-Principles Simulations on the Microscopic Mechanism of Smart Water Enhanced Oil Recovery*

The continuously increasing demand for petroleum and related products calls for the enhancement of crude oil recovery from fractured and low-permeability carbonate reservoirs. Seawater injection has been found to enhance oil recovery and laboratory experiments have revealed that oil recovery can be enhanced by tuning the ionic composition of the injecting brine, but no consensus has been achieved on the underlying microscopic mechanism. In this work, we consider the oil recovery as a friction problem [1] with a thin brine film at the oil/rock interface serving as a lubricant. Inorganic ions, such as Na⁺, Ca²⁺, Mg²⁺, and SO₄^2- modify the water structure and hence are expected to change the lubricant friction property. First-principles molecular dynamics simulations were carried out, revealing the corresponding changes in the friction properties. Comparison with experimental data and a discussion of the atomic-scale interactions underlying the changes in friction will be given.
[1] Gao et al., J. Phys. Chem. B 102 (1998) 5033.