Thickened CO2-Enhanced Oil Recovery in Secondary and Tertiary Oil Recovery Flooding

Summary For this work, we investigated oil recovery performance in horizontal displacement by thickened carbon dioxide (CO2) using poly-1-decene with 20 repeat units (P1D-20) at 1.5 wt% concentration. Depending on temperature and (to a much lesser degree) pressure, the viscosity increase of CO2 was about four to five times. We performed both secondary and tertiary displacements in carbonate rocks at high temperatures of 110°C and 120°C. Most chemical additives become less effective at high temperatures. Two crude oils were used to saturate the cores. In secondary mode, the injection of thickened CO2 gave 35% and 40% higher oil recovery than neat injection in the two crude oils. Two types of tertiary processes were conducted on one of the two oil samples. After water injection, thickened CO2 injection gave 40% additional recovery. In another type of tertiary process, after neat CO2 injection, thickened CO2 was injected. There was a 35% additional recovery. We used a very high-salinity brine to establish initial water saturation. The displacements were carried out at 3,500 psi. Experimental findings highlight the effectiveness of thickened CO2 in mobility control by delaying breakthrough (BT) and enhancing sweep efficiency. In this study, we also explored the application of a slug of 0.3 pore volumes (PV) of thickened CO2 followed by neat CO2. The recovery performance was close to continuous injection of thickened CO2. In all our displacement experiments, neat and thickened CO2 injections were limited to around 1 PV. Efforts toward lower concentration viscosifier chemicals were also explored.