Injection systems involve injection of water or gas into the sub-surface for disposal or stimulation purposes. Water-injection systems include injection of de-aerated seawater, untreated seawater, chlorinated seawater, produced water, aquifer water and combinations and mixing of different waters. NOTE Aquifer water comes from an underground layer of water-bearing, permeable rock from which ground water can be extracted. This water can be used for injection into oil-bearing reservoirs.
Source: API RP 17A Addendum 1, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, December 2010. Global Standards