High-Pressure CO2 Solubility in Crude Oil and CO2 Miscibility Effects on Oil Recovery Performance in Low-Permeability Reservoirs

Abstract

The solubility of CO₂ in crude oil is a crucial parameter that remarkably influences the flood performance of CO₂ for low-permeability reservoirs. However, there is a considerable lack of data on CO₂ solubility in crude oil under high-pressure conditions above 30 MPa in the existing literature, leaving a significant data gap. To address this deficiency, we measured the CO₂ solubility in crude oil under sparsely explored high-pressure conditions (10–50 MPa) and across a broad temperature range (55–100 °C). Our findings revealed a nonlinear saturation trend in pressure dependence, deviating from the near-linear trends reported in prior studies. Using these data, we developed a novel empirical correlation for the CO₂ solubility in crude oil prediction with a deviation of less than 10%, offering improved reliability for high-pressure applications. Additionally, nuclear magnetic resonance (NMR)-based CO₂ flooding experiments provided new insights into the degree of oil utilization and dynamic production performance across different miscibility states. CO₂ near-miscible flooding was recommended as a more viable option in practical applications compared to fully miscible flooding owing to its advantages of good oil recovery enhancement, low propensity for asphaltene precipitation, and relatively low injection cost. This study uniquely bridges the data gap in the existing literature regarding high-pressure CO₂ solubility in crude oil and provides scientific guidance for the exploitation of CO₂ flooding in low-permeability reservoirs.