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Impact of super-critical CO2 on water/oil interfacial tension: A molecular dynamics case study

Yannick Agbor, Barco Yolo

CO₂ flooding is largely controlled by adsorption and interfacial properties between the injected CO₂, oil and formation water. The interfacial tension has an effect on capillary pressure and relative permeability, and thus affects the flow through capillary tubes of porous medium. For tight formations such as the Bakken, the effects of interfacial tension to fluid flow between the formation water and oil is more considerable due to the presence of very small pores (micropores) and capillarity. Previous studies have shown that a decrease in interfacial tension leads to increase in relative permeability.

The water-oil/scCO₂ interfacial behavior has been studied using molecular dynamic simulations. The oil model used is representative of the composition of Bakken oil. The simulations were carried out at reservoir pressure and temperature conditions. The interfacial tension at the liquid–vapor interface of all pure hydrocarbons was calculated and compared with experimental data. The interfacial tension between water-methane/CO₂ at different pressure and temperature conditions is also studied.

From our results, the molecular models for pure components can accurately predict the density and surface tension for six hydrocarbon systems (C₃ – C₈). We observe that increasing concentration of scCO₂ could help reduce the oil-water interfacial tension (IFT) that will aid the oil phase to move along the nanopores. In addition, methane (gas) exhibits a different interfacial behavior with water as compared to liquid hydrocarbons.