CO2 and alkane minimum miscible pressure estimation by the extrapolation of interfacial tension

Abstract

CO2 sequestration in geological formations which can be achieved via injecting the captured CO2 into the pores of depleted oil/gas reservoirs or saline aquifers, is a potential method for reducing greenhouse gas emission. Oil production by CO2 injection, known as the CO2 enhanced oil recovery (CO2-EOR) technique, is a utilization of CO2 with both economic and environmental benefits. The interfacial tension (IFT) and minimum miscible pressure (MMP) of gas–oil system under reservoir conditions are crucial to evaluate the feasibility of this scheme as they determine the eventual improvement of oil recovery efficiency and CO2 storage capacity of reservoir. Thus, it is of great significance to conduct the laboratory experiments on the IFT and MMP of binary systems containing CO2 and oil. In this study, we measured the IFT between CO2 and alkanes with the pendant drop method at a temperature of 298–373 K and pressure of 0.1–15 MPa. The MMP of CO2–alkane was evaluated respectively through the direct observation of gas–oil interface disappearance and by finding the IFT vanishing point using an exponential extrapolation of the IFT values under different pressures. The experimental results indicate that the CO2–alkane IFTs decrease sharply with pressure across the experiment's temperature range. They increase with temperature at higher pressure but decrease at lower pressure in the experimental pressure range. They also increase slightly with carbon number of the alkane at high temperatures. The CO2–alkane IFT exhibits the weakest dependence on the temperature at the high pressure (4–6 MPa) and the high temperature (T > 323 K). Moreover, the linear increase of the CO2–alkane MMP with the temperature was observed and slops increase with the increasing carbon number of the alkane.