CO2-EOR by Effective Oligomer Thickener at 0.3 wt% Concentration in Secondary and Tertiary Processes Using Live Oil

Summary We investigate the effectiveness of a novel oligomer (copolymer of 1-octene and 1-dodecene with 32 repeating units, C8/C12-32) at a concentration of 0.3 wt% as a CO2 thickener for enhanced oil recovery (CO2-EOR). The central objective is to evaluate the effectiveness of increased CO2 viscosity and mobility control in a live oil. Previous work has focused on dead oil, demonstrating the C8/C12-32 performance. In this work, we conduct experiments with a live oil bubblepoint pressure is around 2,800 psi at 120°C, and gas/oil ratio (GOR) is about 635 scf/stb. Experiments are conducted using a horizontal carbonate core with a 1.5-in. diameter and 10-in. length at 3,500 psi and 120°C. The initial brine saturation has a salt content of about 200,000 ppm. The viscosity of CO2 is increased by about 2.5 times at 35°C and 2.1 times at 120°C by the 0.3 wt% oligomer. In the secondary process, viscosified CO2 (visCO2) and neat CO2 are injected for comparison. Neat CO2 gives a recovery of about 63% original oil in place (OOIP), whereas visCO2 yields about 79% OOIP (about 26% additional recovery). Two types of experiments are conducted in the tertiary process, where visCO2 is injected following neat CO2 injection or following brine injection. Neat CO2 injection gives a recovery of about 63%, and visCO2 injection after neat CO2 increases the recovery to 72% (about 16% additional recovery). Water injection gives a recovery of about 57%, and visCO2 injection after water increases the recovery to 72% (about 27% additional recovery). These results are for the live oil. We also present coreflooding data for dead oil. The recovery increase from dead oil is generally higher from CO2 viscosification. The difference between live oil and dead oil displacement may arise from the reduced viscosification, which results from the higher concentration of light hydrocarbons dissolved in the CO2-rich phase. Consistent with our past work, visCO2 in tertiary injection gives high recovery after water injection. Under the same conditions, experiments are also conducted using 1.5 wt% of C10-20 (an oligomer of 1-decene with 20 repeating units, an effective thickener that we used in the past) in a 2-in.-diameter and 10-in.-length core. The additional recovery from the visCO2 injection yields about 28% (secondary) and 25% (tertiary). The effect of alkanes on C8/C12-32 in the CO2-rich phase is weaker than on C10-20, making the new thickener more effective.