Molecular dynamics simulation of electric double layer on tight reservoir surface
The wettability of tight reservoirs is greatly influenced by the microscopic effect of the electric double layer on the reservoir surface.CO2 injection has become a key technology for the efficient development of tight oil reservoirs.To explore how the methods of improving oil recovery in tight reservoirs affect the characteristics and wettability of interface electric double layers,a surface electric double layer model of tight reservoirs was established by using molecular dynamics simulation.The characteristics of the electric double layer on the surface of tight reservoirs at 313 K and 20 MPa were explored,and then the mass transfer effect of supercritical CO2 in the oil-water system under the same conditions and its mechanism of action at the water-rock interface were studied.The analysis results showed that ions in the formation water were affected by different electrostatic interactions and exhibited different density distributions on the rock surface and in the bulk phase.The farther away from the charged rock surface,the lower the net charge density.Supercritical CO2 diffuses into the oil phase to reduce the viscosity of crude oil,and diffuses into the water-rock interface to generate adhesion.CO2 dissolution increases the concentration of H+in the solution,weakening the electrostatic attraction.The synergistic effect of van der Waals force generated by strong hydrogen bonding and electrostatic force makes the water film more stable and enhances water wettability.The research result has certain reference value for the development of microscopic theory of tight reservoirs.
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