Utilization of carbon dioxide for improving the performance of waterflooding in heavy oil recovery

For several years, heavy oil reserves of Western Canada, which are amongst the largest in the world and total more than 5 billion m 3, have been under waterflooding and oil has been produced at very high water-oil-ratios. Despite its shortcomings, waterflooding has been employed because it is relatively a low cost process and is easier to operate compared to other techniques. In many cases waterflooding has been the only easy and low risk option due to the reservoir conditions which have made it impossible for any enhanced oil recovery techniques to be employed. Heavy oil waterflooding is always associated with low recoveries and poor efficiencies and therefore, there is a need for improving the performance of heavy oil waterflooding.;This study consists of twelve core flood tests designed to investigate the effects of CO2 utilization on improving the performance of waterflooding in heavy oil recovery. Two injection methods are used; 1) injection of a slug of 10 to 25% pore volume of CO2 followed by a soak period and then waterflooding, and 2) injection of carbonated water which is prepared by dissolving CO2 in 1% wt. NaCl brine. Experiments were performed at temperatures of 30°C, and at pressures of 500 and 1000 psi. Water injection rates of 1 to 50 ft/day were used to recover heavy oils of 1000 to 2000 cp viscosities.;The results show that, CO2 can be effectively used to make significant improvements in the overall recovery of heavy oil by waterflooding. Post CO2 waterfloodings resulted in incremental recoveries in the range of 5 to 27% of the original oil in place. It was also found that the increase in the volume of the injected CO2 increases the oil recovery. Also, the increase in operating pressure increased the oil recovery. Furthermore, the intermittent injection of water and CO2 resulted in greater recovery improvements compared to the carbonated water injection. It was also found that higher injection rates of water will recover somewhat more oil along with higher volumes of produced water.;Due to its favourable effects, CO2 injection has been accepted in the industry as an effective method of recovery for light to medium oils. But due to the immiscible nature of CO2 and heavy oil, CO 2 injection has not been looked at as a method of recovery improvement in heavy oil reserves of Western Canada. CO2 is highly soluble in both water and oil and therefore, it might be possible to improve the overall heavy oil waterflooding recoveries of these reserves by the utilization of CO2.