Gas injection is a recognized enhanced recovery technique for oil reservoirs, but has been given less attention for gas condensate fields. If a gas condensate is produced by natural depletion, the condensate-gas ratio of the produced well stream will steadily decrease after the saturation pressure is reached. The liquid condensed will stay back in the reservoir and will not be produced.
A laboratory study was conducted for a Middle East gas condensate reservoir fluid. Three different injection gases were used- N2, CO2 and a lean hydrocarbon gas. A gas revaporization experiment was conducted with each gas on the depleted reservoir fluid. The gas revaporization experiments showed that injection of CO2 made the liquid dropout in the PVT cell decrease substantially. Already condensed liquid was revaporized and led to an increased liquid content in the released gas. In small concentrations N2 made the liquid dropout increase, but with a continued injection of N2 the amount of liquid dropout declined. The hydrocarbon gas made the liquid dropout decrease at all concentrations, but to a lesser extent than CO2. An analysis of the results showed that injection of CO2 and a lean hydrocarbon gas may substantially increase the liquid recovery from the actual field, while it is questionable whether N2 injection will have much impact on the liquid recovery.