New Correlations to Calculate the CO2-Oil Interfacial Tension Including the Asphaltene Precipitation Effect

Abstract

Summary COi-based Enhanced Oil Recovery (CO2 EOR) methods have been widely applied and studied in the recent years due to their capability to increase the reservoir recovery factor, as well as an alternative for carbon capture and storage. For instance, CO2 EOR projects have been extensively employed in the Brazilian Pre-Salt reservoirs to take advantage of the high CO2 content in the associated gas. However, CO2-oil interfacial tension (IFT) strongly affects the performance of CO2 EOR processes because the major mechanisms of CO2 injection depend on oil swelling and viscosity, which govern the capillary number and the oil displacement in the porous media. Thus, an accurate modeling of the CO2-oil IFT is required to reach reliable numerical reservoir simulations of CO2 EOR methods. For this reason, this work used CO2-oil IFT and oil characterization data from the literature over pressures up to 55.15 MPa and temperatures from 40 to 70°C – typical conditions of Pre-Salt reservoirs – to develop empirical equations for the CO2-oil IFT prediction. First, new equations to calculate IFT as a function of pressure and CO2 solubility in oil, for dead oils. Afterwards, a sensitivity analysis was performed to evaluate the factors that most affect IFT for live and dead oils, such as pressure, temperature, and oil molecular weight and density. Subsequently, correlations for IFT prediction as a function of the three most relevant factors were proposed. The new equations were validated with additional experimental data from the literature. They are able to predict the CO2-oil IFT under Pre-Salt conditions with high accuracy, providing an absolute average deviation of 6.28% for dead oils and 8.34% for live oils, which are much more accurate than the Parachor model – usually chosen in the numerical reservoir simulators –, which yields 23.38% and 49.69%, respectively. Emphasis should be given to the applicability of the new proposed correlations to calculate IFT in numerical reservoir simulation, once they require low computational efforts, contrasting the overcomplexity of other recently developed equations, which are unfeasible for simulations purpose. Finally, an unprecedented procedure was proposed to examine the effect of the precipitated asphaltenes on the CO2-oil IFT, relating it to the Asphaltene Onset Pressure (AOP) curve. The results are presented with Figures and Tables and properly discussed.