Page 37: of Offshore Engineer Magazine (Jul/Aug 2019)

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Another

Piece of the

Puzzle

BY ELAINE MASLIN ne of the missing links for some fully subsea pro- duction systems has been subsea storage, either for production ? uids, later periodic offtake or production chemicals.

O NOV has been working on a gravity-based subsea storage unit (SSU), based on a design initially devel- oped by Kongsberg. The design, which would compete with a ? oating storage unit (FSU), has now gone through testing and looks set for large scale veri? cation testing, likely in Norway.

The design is based on using a ? exible membrane for oil stor- age, which is contained within a glass reinforced plastic (GRP)

Source: NOV protection structure, that also provides a secondary barrier, in case of a leak. Water is allowed inside the structure, so the sur- 10,000 cubic meters (cu m) to 25,000 cu m for water depth rounding seawater is the same pressure as the stored oil behind above 100 meters. A 10,000 cu m unit – the base case size – the membrane. A center pipe is used for ? lling and emptying, could typically take 40-875 cu m an hour of production and from the bottom of the structure, via a standard ? owline. Should of? oad at 1,000-5,000 cu m an hour, she said. The company there be a leak, a leak detection system would alert the operator has also been working on chemical and produced water stor- and leaked oil would be trapped under the dome. age systems, which could also be needed during ? eld life.

The units can be deployed in clusters that operate together A lot of focus has gone into verifying the membrane that as a hydraulic single unit, but can also be isolated, so that would be used. Following feasibility studies, NOV’s work has the whole storage farm doesn’t fail if a single unit fails, Julie most recently focused on parameter testing using air and then

Lund, subsea engineer and product manager for Subsea Stor- oil in scale tank models, which completed in early June at the age Systems at NOV, told the Underwater Technology Confer- Institute for Energy Technology (IFE) near Lillestrøm, Norway. ence (UTC) in Bergen earlier this year. This veri? ed the behavior of different membranes and geom-

Lund says that subsea storage could offer lower capex and etries and how oil ? lled and drained from the scale model tanks. opex than an FSU, as well as a lower environmental footprint. NOV now plans to do a large-scale veri? cation test working

NOV is pitching 20-year design life units at sizes between with Equinor and The Oil & Gas Technology Center in the UK.

JULY/aUGUST 2019 OFFSHORE ENGINEER 37