Thermodynamic calculation studies on oil composition and water presence effect on the minimum miscibility pressure of the CO2/two-components oil system

Abstract

Minimum Miscibility Pressure (MMP) is a key parameter for guiding the CO₂ Enhanced Oil Recovery (EOR) as well as carbon geological storage applications. In this work, a thermodynamic calculation study is performed concerning the oil composition and the water presence effect on the MMP properties of the CO₂/multicomponent oil system under various temperatures. Two-components oils with different n-C₁₄H₃₀ and n-C₁₉H₄₀ ratios at 7:3, 6:4, 5:5, 4:6 and 3:7, are employed to reveal the oil composition effect on MMPs of CO₂/oil system. Via introducing saturated water into CO₂, the effect of water presence on MMPs of the CO₂/oil system is studied as well. Thermodynamic calculation results show the MMP of the CO₂/two-components oil systems increases from 8.5 MPa to 9.8 MPa, 10.1 MPa to 11.2 MPa, 11.6 MPa to 12.6 MPa, 12.9 MPa to 13.8 MPa, and 14.2 MPa to 15.0 MPa, together with the increasing portion of the heavier C₁₉ oil component from 30 % to 70 % at various temperatures of 40 °C, 50 °C, 60 °C, 70 °C and 80 °C, respectively. Calculation results also reveal the presence of the water component would reduce the MMPs of the CO₂/oil system by 0.2–0.8 MPa compared with the water absence case in the studied oil component and temperature conditions. In particular, the water presence effect on MMP reduction is more significant for the oils with higher portion of heavy components.