EFFECT OF NITROGEN ON THE SOLUBILITY AND DIFFUSIVITY OF CARBON-DIOXIDE INTO OIL AND OIL-RECOVERY BY THE IMMISCIBLE WAG PROCESS

In the immiscible displacement of oil by carbon dioxide gas, the solub ility and diffusivity of carbon dioxide are important factors that det ermine the efficiency of the process, because an increase in the carbo n dioxide solubility and diffusivity into oil leads to an increase in oil recovery. It is shown by experimental studies that the solubility and diffusivity of carbon dioxide into oil are governed by the saturat ion pressure, reservoir temperature, composition of the oil and purity of the gas. The solubility and diffusivity of carbon dioxide into Abe rfeldy heavy oil were measured, using impure carbon dioxide gas contai ning nitrogen as the main contaminant gas. It was noted that increasin g the concentration of nitrogen in the carbon dioxide stream decreased the solubility and diffusivity of carbon dioxide in oil, consequently leading to a reduction in the swelling of the oil by carbon dioxide. Displacement experiments were also conducted to observe the effect of using impure carbon dioxide in place of pure care bon dioxide in the i mmiscible displacement WAG process. It was noted that the presence of nitrogen in carbon dioxide adversely affected oil recovery by the proc ess and that increasing the nitrogen concentration up to 30 mole% coul d result in 10% loss in oil recovery.