Stability and Enhanced Oil Recovery Performance of Co2 in Water Emulsion: Experimental and Molecular Dynamic Simulation Study

Abstract

Enhanced oil recovery by CO2 flooding is conducive to the development in terms of energy and environment. However, the geological storage capacity and oil recovery of CO2 is relatively low because of its low viscosity, gravity segregation and reservoir heterogeneity. CO2 in water (C/W) emulsion can reduce CO2 mobility and increase the volumetric efficiency of CO2. In this paper, the stability and recovery performance of C/W emulsion were investigated. The results show that the C/W emulsion formed by AOT was more stable than the C/W emulsion formed by SDS. CO2 molecules were difficult to penetrate through the AOT layers due to two hydrophobic chains in AOT molecules. Emulsion stability tests show that the C/W emulsion was more stable with higher pressures and lower temperatures. The hydrophobic chains of AOT were closely packed at high pressure thereby increasing the AOT layer thickness, which can increase the stability of C/W emulsion. The enhanced oil recovery by C/W emulsion at 8 MPa and 10 MPa were 23.72% and 34.88%. The density, viscosity and asphaltenes content of the produced oil after C/W emulsion flooding were much lower than the original crude oil. The asphaltenes content in residual oil was higher than that in the original crude oil and produced oil. The micromodel test and MD simulation study indicate that CO2 could extract light components including saturates and aromatics out of the crude oil. As a result, the asphaltenes molecules would aggregate and precipitate. The light saturates molecules absorbed to the oil-water interface could form oil in water droplet and produce during the C/W emulsion flooding. The heavy components including resins and asphaltenes were remained in the oil phase.

Keywords: ScCO2 flooding, CO2 in water emulsion, Enhanced oil recovery, MD simulation