EFFECT OF PRESSURE ON IMPROVED OILFLOOD RECOVERY FROM TERTIARY GAS INJECTION

Twenty-eight tertiary gas-injection corefloods were conducted to defin e the pressure/recovery curves for five crude oils. These results have been compared with slim-tube recovery tests using the same five reser voir fluids. Field-scale CO2 floods have been or are currently under w ay in three of the studied reservoirs (S, H, and M). The other two res ervoirs (F and A) have been considered for CO2 and hydrocarbon-gas inj ection, respectively. The results for the four CO2 injection systems c onsistently 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 us e short cores, it is expedient to use an external transition-zone gene rator. A method has been developed that successfully circumvents the o il resaturation problem caused by most transition-zone generators.