The Displacement of Residual Oil By Carbon Dioxide

Displacement of a 36'API W. Texas oil from watered-out cores with carbon dioxide was investigated at reservoir conditions of 90/sup 0/F and 1,250 psig. Phase behavior of the CO/sub 2/-W. Texas oil system was also investigated. The objectives of the study were (1) to determine the oil recovery efficiency, and (2) to improve understanding of the oil recovery mechanisms, especially in relation to the phase behavior. The phase behavior studies indicate that CO/sub 2/ efficiently swells the oil and forms 2 equilibrium liquid phases with the oil. Significant amounts of light and intermediate hydrocarbons are shown to be extracted into the CO/sub 2/-rich liquid phase from the oil phase. The CO/sub 2/ displacement studies conducted on watered-out cores indicate that a continuous CO/sub 2/ drive can achieve a maximum recovery of 69% of residual oil from a 6-ft Berea core and 66% from a 20-ft sand-packed core. The minimum CO/sub 2/ slug size required in a water-propelled CO/sub 2/ drive for maximum recovery is 0.42 PV for the Berea core and 0.27 PV for the sand-packed core. In both cases, the required slug sizes are slightly greater than residual oil saturations. An analysis of the results of the phase behaviormore » and displacement studies indicates that CO/sub 2/ swelling and CO/sub 2/ extraction of oil are responsible for recovering residual oil.« less