The physical models, cylindrical tube (1-D) and rectangular box (3-D), were used to examine the effects of simultaneous injection of CO2 and CH4 together with steam on the recovery of 12.4 °API gravity heavy oil mixed with unconsolidated limestone.

The results of 18 experiments showed that gas-steam injection was a promising technique. Gas/steam ratio was found to be a significant factor among the studied variables in heavy oil recovery. The optimum gas/steam ratio that maximized the recovery was about 9.4 cc/cc for both steam-CO2 and steam-CH4 processes in one-dimensional model. It was 8.7 cc/cc for steam-CO2 process in 3-D model.

At 1.5 pore volumes of steam injected; the oil recoveries were 66.5 % of OOIP for steam-CO2, 60.4 % of OOIP for steam-CH4 and 50.9 % of OOIP for steam alone tests in 1-D model and they were 49.9 % of OOIP for steam-CH4, 36.2 % of OOIP for steam-CO2 and 21.7 % of OOIP for steam alone tests in 3-D model. The lower residual oil saturations were obtained in gas-steam injection tests, compared to the values obtained with steam alone.

The injected non-condensable gas created a permanent gas phase across the top of the model therefore heat arrived to the producing well earlier than steam alone test. The depression of steam temperature was also observed due to the presence of non-condensable gas.

Keywords:
upstream oil & gas, heavy oil, recovery, steam oil ratio, non-condensable gas, experiment, oil recovery, co 2, enhanced recovery, reservoir
Subjects:
Well & Reservoir Surveillance and Monitoring, Improved and Enhanced Recovery, Unconventional and Complex Reservoirs, Gas-injection methods, Thermal methods, Oil sand, oil shale, bitumen
Copyright 2004, Society of Petroleum Engineers
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