Effect of pressure on improved oilflood recovery from tertiary gas injection

Twenty-eight tertiary gas-injection corefloods were conducted to define the pressure/recovery curves for five crude oils. These results have been compared with slim-tube recovery tests using the same five reservoir fluids. Field-scale CO2 floods have been or are currently under way in three of the studied reservoirs (S, H, and M). The other two reservoirs (F and A) have been considered for CO2 and hydrocarbon-gas injection, respectively. The results for the four CO2 injection systems consistently showed that oil recovery decreases dramatically below the minimum miscibility pressure (MMP) exactly like slim-tube tests, while the recovery in the hydrocarbon-gas injection system decreased almost linearly with decreasing pressure both above and below the MMP. To use short cores, it is expedient to use an external transition-zone generator. A method has been developed that successfully circumvents the oil resaturation problem caused by most transition-zone generators.