Recovery of Viscous Oil Under High Pressure by CO2 Displacement: A Laboratory Study

Abstract

ABSTRACT Laboratory coreflooding experiments were performed to investigate the technical feasibility of the use of the CO2 flooding process under immiscible conditions for the recovery of viscous oil. A stock-tank oil of 22° API gravity was recombined with solution gas at a gas-oil ratio (GOR) of 48 scf/bbl. The CO2 flooding tests were conducted in a consolidated Berea sandstone core under simulated reservoir conditions. The viscosity of the recombined oil at reservoir temperature (152° F) and pressure (2,500 psig) was 50 cp. Experimental results show that the oil viscosity was reduced to 8 cp, and the oil volume was swelled to 1.2 times the original volume after saturation with CO2 at the testing condition. Oil recovery from a 2-in.-diameter and 2-ft-long core by CO2 flooding for the testing oil was unusually high even under Immiscible conditions. The ultimate oil recovery from a secondary CO2 flood is as much as 60 % of the original oil in place (OOIP), which is higher than the average oil recovery from a secondary waterflood, 44 % OOIP. After waterflood, a continuous injection of 1.5 PV of CO2 recovered an additional 33 % OOIP. The CO2 utilization factor was 11.7 Mscf/bbl of additional oil recovered. The CO2-alternate-brine injection method significantly delayed the breakthrough of gas and provided a slightly higher oil recovery and more efficient CO2 utilization than the continuous CO2 injection method. Overall, the ultimate residual-oil-saturation (Sor) was reduced to 18% PV by all of the above CO2 injection methods.