Experimental Studies On CO₂ Assisted Steam Injection For Super-heavy Oil Reservoir Development

It is very difficult to exploit the super-heavy oil reservoir for its higher viscosity,and less effective by steam stimulation method. In order to enhance the recovery of super-heavy oil reservoirs, the method of CO2 assisted steam stimulation is proposed. The effect of CO2 on bubble point pressure, solution gas-oil ratio, formation volume factor of heavy and super-heavy oil was studied by the newly-improved PVT apparatus. The viscosities of heavy and super-heavy oil dissolved by CO2 under high pressure and temperature were measured by self-designed high pressure visco-meter. The factors effecting the viscosity of CO2–heavy or super heavy oil systems were also studied. The oil recoveries were compared by steam stimulation and CO2 assisted steam stimulation using steam flooding equipment and sand-packed models. The effect of injection pressure of steam was analyzed. Experiments show that the solubilities of CO2 in heavy and super-heavy oils are very low. The viscosity of CO2–heavy or super-heavy oil systems decreases by up to 30%. Compared with steam stimulation, the oil recovery increases from 10% to15% by CO2 assisted steam stimulation. The displacement mechanisms of CO2 injection and steam stimulation are analyzed. CO2 dissolution in heavy oils helps to improve flow performance of heavy oil, CO2 also helps to improve the heat utilization of steam to some extent compared with steam injection only. CO2 assisted steam stimulation for super-heavy oil recovery is a brand new technique and very effective for enhanced super-heavy oil recovery.