A Field Pilot Test on CO2 Assisted Steam-Flooding in a Steam-flooded Heavy Oil Reservoir in China

It is challenging to enhance heavy oil recovery in the late stages of steam flooding. This challenge is due to the reduced residual oil saturation, the high steam-oil ratio, and the lower profitability. A field test of CO2-assisted steam flooding technology was carried out in the steam-flooded heavy oil reservoir in the J6 block of Xinjiang oil field (China). The field test showed a positive response to the CO2-assisted steam flooding treatment including a gradually increasing heavy oil production, a rise in formation pressure, a decrease in water cut, etc. The production wells in the test area mainly exhibited four types of production dynamics, while some production wells showed production dynamics that were completely different from those during steam flooding. After being flooded by CO2-assisted steam flooding, these wells exhibited a gravity drainage pattern without steam channeling issues, and hence could yield a stable oil production. Meanwhile, emulsified oil, together with CO2-foam, was observed to be produced in the production well, which agreed well with what was observed in the lab-scale tests. The reservoir-simulation-based prediction in the test reservoir shows that the CO2-assisted steam flooding technology can reduce the steam-oil ratio from 12 m3 (CWE)/t to 6 m3 (CWE)/t and yield a final recovery factor of 70%.