Nitrogen has been found to be a suitable recovery agent for conventional oil with API gravity larger than 35 that provides the reservoir pressure is above the minimum miscibility pressure and the reservoir oil contains a high concentration of intermediate hydrocarbon components. Nitrogen has been found to achieve dynamic miscibility at high pressures. The miscibility obtained by nitrogen injection in light crude oil reservoir is a conditional miscibility, where the fluids are not miscible on first contact, but form two phases, with one of the fluids absorbing components from the other. After sufficient contacts and exchanges of components, at minimum miscible pressure, the system becomes miscible.
The main purpose of this study is to investigate, the effect of temperature, composition of the reservoir fluid and injected gas, on the MMP of nitrogen injection in light oil reservoir by a simulator. The injected gas is pure Nitrogen or a combination of nitrogen with other gas like propane. The effect of varying the percentage of nitrogen and CO2 in the injection gas mixture on MMP has been previously investigated by experiment.
Results of the Simulation have shown that the most important factor to achieve miscibility between nitrogen and reservoir oil is the amount of light and intermediate components in the oil. Increasing the intermediate components and decreasing the methane content decrease the MMP. Nitrogen develops miscibility of oil by the same mechanism as methane (vaporizing gas drive). With sufficient amount of methane in oil reservoir, MMP of nitrogen and methane injection is almost the same but decreasing the methane content causes difference. Studies have shown that injecting nitrogen-propane combination will decrease MMP but combining nitrogen with methane does not have significant effects on the MMP. Result show that MMP of nitrogen increases slightly when temperature decreases.