Application of CO 2 -based vapor extraction process for high pressure and temperature heavy oil reservoirs

A considerable portion of hydrocarbon resources in the world comprises heavy oils. Due to the high viscosity of these oils, production from these resources is difficult and requires especial enhanced oil recovery techniques. Carbon dioxide (CO2) based vapor extraction (VAPEX) process has recently been introduced as an effective method for recovery of heavy oils. However, this method has not yet been implemented in oil fields. Previous studies on CO2-based VAPEX were performed in small cells under low pressure (<9400kPa) and temperature (<60°C) conditions. In this study, the CO2-based VAPEX process was simulated for a real heavy oil reservoir to determine the application of CO2 as a non-condensable carrier gas, co-solvent, and solvent at high pressure (20,685kPa) and temperature (82.2°C) condition. Different solvent mixtures including propane (C3), butane (C4), methane (C1), and CO2 were utilized. It was found that in high pressure and temperature conditions, CO2 is not a good non-condensable carrier gas due to the miscibility of solvent mixtures (C3/C4+CO2) with the reservoir oil. In contrast, CO2 application for heavy oil recovery in such condition is similar to C3. The simulation results demonstrated that replacement of C3 with CO2 in the solvent mixtures has led to the recovery of the same amount of oil. This replacement has also caused a higher reduction in the heavy oil viscosity to obtain. Thus, CO2 can be considered as a good alternative for C3 in the VAPEX process specially for use in high pressure and temperature reservoirs. The outcomes from this research provide a new way for recovery of heavy oils by applying CO2 as a solvent in reservoirs that have high pressure and temperature.