Abstract

This paper presents the results of a laboratory study investigation the capacity of CO2 to extract hydrocarbons from crude oils. The effects of pressure, temperature and oil composition on the extinction capacity of CO2 were studied. Extraction experiments using CO2 with Sulimar Queen stock tank oil and Spraberry sepetor oil samples at pressures between 1000 and 1900 psig were performed each at 95°F and 138°F. The experiments were performed by continuously injecting CO2 through 500-cc of oil placed in a 1.15 liter extraction vessel while continuously producing the upper or CO2 phase which contains the extraction products.

CO2 extraction capacity was found to be a strong function of pressure and temperature. The extraction capacity increases with increasing pressure and decreases with increasing temperature. For the oils used in this study, the presence of solution gas in the oil does not affect the CO2 extraction capacity.

A CO2-Sulimar Queen oil extraction experiment at constant pressure and temperature of 1200 psig and 95°F, respectively, was performed for an extended period of time to determine the maximum oil recovery that can be achieved by CO2 extraction. It was found from the experiment that CO2 could recover at least 70 vol % or 64 wt % of the original oil in place. The CO2 extraction capacity decreased from around 0.3 g oil/g CO2 injected at the beginning of the extraction to 0.005 g oil/g CO2 injected at the time of termination.

Comparison of the extraction and slim tube tests results shows that the slim tube minimum miscibility pressures (MMPs) are near the pressure range at which a drastic increase in CO2-oil extraction rate occurs, which implies that CO2 extraction is a major factor in CO2-oil miscibility development. The comparison also shows that the extraction experiment appears to have promise as a good CO2-oil MMP estimation method.