Investigating the Effect of CO2 Flooding on Asphaltenic Oil Recovery and Reservoir Wettability

Miscible and immiscible flooding with CO2 of oils containing asphaltene for chalk reservoir is investigated. Oil recovery from model oil and crude oil (30 degrees API gravity), containing 0.35 and 10 wt % asphlatene, respectively, is addressed. n-Decane is used as a reference oil and showed an increase of recovery from 81 to 89% at 50 degrees C and 90 bar and 80 degrees C and 140 bar, respectively. Both model and crude oils showed a reduction in the oil recovery from 78.92 to 70.4% and from 37.6 to 36.6%, respectively, at the same conditions as that for the reference oil. The insignificant change in the oil recovery between the two conditions for the crude oil may be due to the high asphaltene content (10%). A model based on the solubility theory is developed to account for the effect of CO2 flooding and is verified using literature data for CO2 flooding. The average deviations of the model for the miscible flooding from the experimental are 15 and 18% for this study and literature data, respectively. The relative contribution of CO2 on asphaltene precipitation because of miscible CO2 flooding is compared to that for the pressure and temperature effect. On the basis of the approach in this work and available data from literature, CO2 critical content lies between 42 and 17 mol % in the liquid phase, with an average value of about 33 mol %.