Seawater Springs

Seawater injection is one of the jigsaw pieces making up the subsea processing puzzle. Elaine Maslin reports on Saipem’s Springs technology.

Springs, how it might look subsea.  Image from Saipem.

Italian contractor Saipem has been working on a subsea seawater injection technology for the last 10 years and it’s now ready to industrialize it, with first commercial use targeted for 2019.

Stephane Anres, innovation & technology development, technical area coordinator – subsea systems, Saipem, told the Underwater Technology Conference in Bergen about the technology.

“Most of us believe subsea systems will play a large role in subsea production,” he said. “This is why Saipem, 10 years ago, started to develop its own systems, including seawater treatment.”

Having seawater treatment reduces the need for topsides space and or modifications, Anres says. “It just needs a power and control unit.” This also ties into the all-electric vision operators, including Total, are targeting. In fact, Saipem, along with Total and water treatment specialist Veolia, have jointly qualified the technology.

This technology is called Springs, standing for “subsea process and injection gear for seawater.” Its role is sulfate removal for satellite fields more than 10km from a floating production (FPSO) unit and existing fields without the need for major FPSO modifications, i.e. just a subsea power and control unit is needed topside, not a full seawater treatment facility, Anres says. Removing the sulfate prevents scale formation and reservoir souring.

“Seawater is crucial to treat before injection because it contains barium and calcium and could cause souring,” Anres says. “If it’s not removed, sulfates come out as scale.”

The system would be able to handle 10,000-80,000 b/d of seawater, he says. Seawater intake would be about 100m above the Springs unit, which would comprise a pumping module, umbilical, instrumentation and control, a pre-filtration module for solids, and a membrane module, plus chemical storage – the chemicals are used to mitigate/reduce fouling of the filtration membrane. It’s all modular, Anres says.

The membrane module contains nano-filtration membranes. The concentrated sulfate brine produced by the unit is removed using a dedicated reject line for disposal to sea. De-sulfated water is re-injected for pressure support. The chemical unit would be periodically refilled (max, once per year) with non-oxidizing biocide to maintain anti-fouling, which would be batch dosed according to project requirement.

The membrane has been qualified to 3000m water depth. In laboratory testing, the membrane was tested to 4° C. It was then incorporated into a subsea test unit, which was taken offshore Congo in 2014 for trials in 600m water depth from the Alima floating production unit. Test results were water samples with sulfate content always lower than the 40mg/l specification, Anres says. No plugging was experienced with the inlet screen and there was no issue with pre-filtration treatment, he says. Since then, Saipem has been updating and optimizing the system, based on the test results.

The first commercial use is anticipated in 2019, Anres says.

“The main qualification tasks have been completed. We have started industrialization of the system, defining and securing the supply chain. We have entered several partnerships with different suppliers, for example Siemens on the subsea control system.”

For commercial sites, the existing subsea test unit could be deployed to optimize the design of a particular field’s unit, Anres says.