The world's first full-scale subsea plant for production of sulphate free or low salinity water for IOR and EOR purposes has been designed, procured, constructed, and commissioned. This has been achieved with the involvement and support of an original equipment manufacturer, the Norwegian Research Council, and several offshore oilfield operators. The full-scale subsea treatment plant has undergone qualification in accordance with API 17N, and this paper shares key design aspects of the plan, operational experience, and the water quality results achieved.

Subsea seawater treatment for water injection has several inherent advantages compared to topside treatment. One significant aspect is the increased flexibility afforded to reservoir engineers in improving effective reservoir management by providing the opportunity to implement any desired water injection capacity, anywhere and anytime. In addition, the ability to provide 'tailor made' water for injection into oil reservoirs is seen as a game changing opportunity for offshore oilfield production companies wishing to produce more, produce faster, and produce cheaper.

The process advantages of the seawater treatment plant being on the seabed allows for a design that is simplified compared to a corresponding topside plant. This system design is explained in the paper and how it translates into improved reliability and availability. The all electric design also has the capabilities to be installed, moved, and reused on the seabed with minimum impact on topside infrastructure.

This paper provides information that has not been presented before about the novel subsea seawater treatment process. It shares commissioning and operational knowledge gained during a six month test period and includes water quality results achieved at progressive points through the treatment plant. The ability to operate a water treatment plant on the seabed necessitates instrumentation and control that provides good condition monitoring of equipment and the ability to check and control water quality. The novel methods that have been employed and tested on this treatment plant are discussed.

The treatment plant has been fully tested and is now available to clients for installation and operation on an offshore field. Lessons learnt are shared along with showing how the treatment design can be used to provide high-quality water on a wide range of field applications at any stage of a field's lifetime.

There are several aspects of the design that reduce the health, safety and environment (HSE) impact of water injection in general, including; lower power consumption (reducing carbon footprint) and no (or significantly reduced) liquid chemical requirement; hence, lower handling exposure for operators.

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