Water injection wells may be located on- and offshore, to increase oil recovery from an existing reservoir.
This reduces the potential of causing formation damage due to incompatible fluids, although the risk of scaling or corrosion in injection flowlines or tubing remains.
However, the processing required to render produced water fit for reinjection may be equally costly.
Seawater may be the most convenient source for offshore production facilities, and it may be pumped inshore for use in land fields.
Where possible, the water intake is placed at sufficient depth to reduce the concentration of algae; however, filtering, deoxygenation, treatment with a biocide is generally required.
Aquifer water from water-bearing formations other than the oil reservoir, but in the same structure, has the advantage of purity and chemical compatibility where available.
Filters clean the water and remove impurities, such as sediments, shells, sand, algae and other biological matter.
Bacterial growth in the reservoir can produce hydrogen sulfide, a source of production problems, and may block the pores in the rock.
The filtered water flows down the de-oxygenation tower, splashing onto a series of trays or packing causing dissolved air to be transferred to the gas stream.
An alternative or supplementary method, also used as a backup to deoxygenation towers, is to add an oxygen scavenging agent such as sodium bisulfite and ammonium bisulphite.
Membrane contactors bring the water into contact with an inert gas stream, such as nitrogen, to strip out dissolved oxygen.
Membrane contactors have the advantage of being lower weight and compact enabling smaller system designs.
Air was stripped from the water by an upflow of fuel gas, gas/air was routed from the top of the vessel to the flare.
[6] The table shows the number of water injection wells on a selection of offshore installations mainly in the North Sea.