Injecting seawater into reservoirs for maintenance of reservoir pressure and increased oil recovery (IOR) is a long established and common practice. Treatment of the water before injection is however essential to avoid plugging and souring of the reservoir. The treated seawater is injected into the main field reservoir through platform-based injection wells, or can be transported out to subsea injection wells through long flowlines. While this approach has served the industry for many years, it does impose some challenges, mainly implications associated with being able to effectively drain a field.

As an alternative solution to enhance IOR and maximise production, SWIT has been under development and testing since 2003. Since then it has been awarded four patents and won an innovation award at ONS in 2006.

As part of its continued development, full scale subsea pilot plant trials were required and ITF worked in collaboration with Well Processing to secure industry funding from several international oil companies for field trialling. This also brought about the opportunity to secure further funds from DEMO 2000 and marked the first time that the two bodies have worked in conjunction to secure support for a Joint Industry Project (JIP).

The 18 month long SWIT JIP was launched in December 2008 with support from four major oil and gas operators and DEMO 2000. The technology allows for significant reduction in solids content, provides two independent methods for ‘on line’ sterilisation of seawater – electro-chlorination and a new method for sterilisation via hydroxyl radical generation - and also includes system sterilisation.

Well Processing developed the SWIT technology to allow reservoir engineers the freedom to think outside the box. Because a topsides water treatment and injection plant is reliant on the data gathered from initial appraisal well information, it may be inadequate for the fields needs over its entire lifetime.

SWIT gives freedom of choice with respect to the number and location of injection wells – it allows for injection of as much treated seawater as required, where required – without typical host platform restrictions. This technology essentially allows the decision on water injection needs to be delayed until the reservoir is up and running because operators can see how a reservoir reacts then provide water injection as required rather than having to estimate future requirements and design them into the platform at the outset.

The Subsea Control Unit has been now been assembled and tested. The submerged testing was successfully held in July 2009 with full functionality and communication with the equipment installed in the SWIT unit. Latest test results show that SWIT treatment is having a significant effect on delaying formation of the biofilm. Other results continue to show excellent disinfectant results and a continuous reduction in solids content. A new circulation pump has been installed and flow through the instrument is now steady.

In July 2010, the SWIT plant passed one year of operation on the seabed. The treatment plant successfully completed its objectives of operating on the seabed through a full years seasonal variations. The water treatment results have been very encouraging, proving that SWIT has a significant effect on: delaying the formation of biofilm, excellent disinfectant results and a continuous reduction in solids content. The inherent simplicity of the system has also enabled a 99,6% uptime. A further proposal will be circulated to ITF Members to use the ongoing SWIT water treatment pilot plant to provide feed water to test improvements in membrane lifetime and also as a new means of cleaning that may enable the whole treatment process to be situated on the seabed.

SWIT expands the choices available to operators and allows for injection of as much treated seawater as required, where required – without the restictions and limitations associated with using a host platform. The technology is being continually developed and other applications for SWIT include boosting pressure in older reservoirs and the development of satellite fields that would otherwise be uneconomical.