Nitrogen flooding can be an important Enhanced Oil Recovery (EOR) method if the certain conditions are present in the production zone:
- The reservoir oil must be rich in the lighter hydrocarbons ethane through hexane (C2-C6) that is in hydrocarbons that have an API gravity higher than 35 degrees.
- These light oils should have a high formation-volume factor that is the capability of absorbing added gas under their present conditions.
- The oil in the production zone should be low in methane (C1).
- The reservoir should be deep enough to withstand the injection pressures, sometimes in excess of 5,000 psi. This is necessary for the oil to attain miscibility with nitrogen without fracturing the producing formation.
Nitrogen is now more attractive for flooding because it can be manufactured on site at less cost than other alternatives. Since it can be extracted from air with Nitrogen Membrane units, there is an unlimited source, and being completely inert it is noncorrosive. In general, when nitrogen is injected into a reservoir, it forms a miscible front by vaporizing some of the lighter components from the oil. This gas, now enriched to some extent, continues to move away from the injection wells, contacting new oil and vaporizing more components, thereby enriching it still further. As this action continues, the leading edge of this gas front becomes so enriched that it goes into solution, or becomes miscible, with the reservoir oil. At this time, the interface between the oil and gas disappears, and the fluids blend as one.
Continued injection of nitrogen pushes the miscible front (which continually renews itself) through the reservoir, moving displaced oil toward production wells. Water slugs can be injected alternately with the nitrogen to increase the sweep efficiency and oil recovery.
At the surface, the produced reservoir fluids may be separated, not only for the oil but also for natural gas liquids and injected nitrogen.