Enhanced Oil Recovery Nitrogen Injection System
Nitrogen has been used successfully for more than 20 years in pressure maintenance and has now gained prominence over the last decade as the injectant of choice for enhanced oil and gas recovery. Applications include using nitrogen as a driving force for costly and limited carbon dioxide, and in some cases for miscible displacement. The displacement of gas cap gas, the production of attic reservoirs, the cycling of condensate reservoirs, reservoir pressure maintenance, “huff and puff” cyclic process, dilution of high BTU natural gas, and many other applications that are currently under consideration. Nitrogen provides a higher reservoir displacement volume per standard volume of nitrogen than any other gas injectant; that is, it provides the lowest volume requirement for pressure maintenance.
The injected nitrogen will not react with the reservoir fluids or compressor lube oils to produce undesirable by-products and precipitates. Moreover, the formation of anaerobic material in the formation is minimized, thereby reducing the need for biocide inhibitors.
Nitrogen is also non-corrosive. Therefore, no special metallurgy is required for the injection equipment, no corrosion inhibitors are needed to protect the existing equipment, and no materials must be replaced on the existing production equipment. It is environmentally compatible and does not contribute to the greenhouse gas effect when injected and released to the atmosphere. It is also readily available from air.
Eventually, nitrogen will break through into the produced associated gas. A nitrogen rejection unit (NRU) will then be needed to ensure the product gas is marketable. This breakthrough generally occurs later than if CO2 had been used. Based on available nitrogen rejection studies, these facilities add approximately 50 to 60 cents/Mcf to the cost of using nitrogen. Even with the added cost for future nitrogen rejection facilities, the nitrogen injection option is still less expensive than injection of any other kind of gas.