Experimental Determination of the Interfacial Tension and Swelling Factors of Bakken and Duvernay Oils with CO2, Impure CO2, Methane, Ethane, and Propane

Gas capture and injection into oil reservoirs can improve oil recovery and store greenhouse gases in the subsurface, but the impact of the injected gases on the oil in the reservoir must be understood. This study determines the changes in the oil properties including the minimum miscibility pressure (MMP), first contact miscibility pressure (FCM), and swelling factor Duvernay are equilibrated with CO2, CO2 with 4.9% SO2, methane, ethane, and propane. The calculated MMPs for CO2-SO2 were lower than CO2 for all three oils, and CO2-SO2 caused both Bakken oils to swell more than pure CO2, indicating SO2 in CO2 may be beneficial for miscible gas injection operations. The calculated MMPs and FCMs of methane, ethane, and propane decreased in that order for each of the oils. The MMPs and FCMs were greater for North Dakota Bakken compared to Saskatchewan Bakken due to the higher reservoir temperature of the North Dakota Bakken. Methane did not cause any of the oils to swell, whereas ethane and propane caused all three oils to swell. Simulated distillation analysis of the oil samples after the swelling experiment showed that light and intermediate hydrocarbons moved from the oil to the surrounding phase even at pressures below the MMPs, which may impact the performance of a gas injection EOR project by leaving the heavier fractions of oil in the reservoir. This work provides a better understanding of the impact of gas injection on the oil properties that could lead to improved hydrocarbon recovery if further work to examine the impact the calculated MMPs have on oil recovery and the impact of the precipitation of heavy oil compounds is completed.

Automated summary

Gas injection in oil reservoirs can enhance oil recovery, but its impact on oil properties must be evaluated. This study investigated the changes in oil properties when equilibrated with various gases including CO2, CO2-SO2, methane, ethane, and propane. The results demonstrated that CO2-SO2 may be more beneficial for miscible gas injection compared to pure CO2. Additionally, methane did not cause oil swelling, while ethane and propane induced oil swelling.