Treated seawater is usually injected into oil wells during the extraction of hydrocarbons for pressure support and increased oil recovery. Seawater for injection can be treated topside or on the seabed. For any seawater treatment system, the water intake and pre-treatment stage is key to enable long term maintenance free operation.

A subsea SWT system provides a number of advantages such as freedom from topsides restrictions with weight & space, deferred CAPEX investment, flexibility in reservoir drainage strategy, enable marginal field development, allow unmanned operations, reduction in chemical consumption and carbon foot print.

NOV’s subsea seawater treatment technology utilizes SEABOX modules as pre-treatment (disinfection and solids settling). Lessons learnt from previous operations indicated that a self-cleaning (de-scaling) treatment cell (EC & HRG) is required to operate subsea and maintenance free for minimum four years.

Therefore, a full scale self-cleaning, maintenance free treatment system has been tested continuously for 6 months with funding and support from Equinor. Very good results have been achieved, confirming the longevity. This presentation will cover test set up, operational procedure for long term subsea operation, test results, findings and conclusions to enable minimum 4 years maintenance free subsea operation (without the need for system retrieval or cleaning).

The system, comprising of treatment cells, power supplies, control system and test set up is identical to what is intended to be actual field application.

To be Co-authored with Equinor