NOV's Christian Dyhr, Global Sales & Marketing Director for Subsea Production Systems, discusses how NOV's subsea storage unit (SSU) can revolutionize offshore oil production.
SSUs for oil storage were originally developed and qualified by Kongsberg Subsea Products prior to NOV's acquisition of the business.
The units provide flexibility, reliability and dramatic cost reduction to operators everywhere compared to topside storage.
Particularly valuable to marginal oil fields and oil fields in extreme conditions, the patented SSU enables storage of crude oil, chemicals and produced water at the seafloor.
The technology complements NOV's APL offloading system, creating a single package of subsea infrastructure, reducing cost and risk for the customer base. From a design and construction perspective, SSUs are an elegantly simple, high-tech answer to the question of how to store oil without having more costly and riskier floating storage units (FSUs).
An SSU consists of a structure that employs the concept of a flexible bag protected by a dome for storage on the sea floor, and thereby eliminates problems with emulsion layer and bacteria growth. It can be placed at any water depth and is adjustable in size depending on the needs during the development and expansion of the field.
The seawater outside the protection structure surrounds the flexible bag through free-flow seawater openings in the protecting structure, such that the hydrostatic pressure acts directly on the stored fluid, hence the internal pressure is equal to the external seawater pressure. The oil is stored at a hydrostatic pressure greater than the oil vapor pressure, thereby preventing gas separation. The partially stabilized oil is offloaded to a shuttle tanker with capabilities of handling such a vapor pressure (liquefied petroleum gas). The solution is not dependent on offloading frequency and can be customized to fit field requirements.
SSUs can also be utilized to store chemicals (i.e. monoethylene glycol (MEG)) and processed water. Using a SSU to store MEG eliminates the need for MEG flowline use on a cooled-down manifold when the production has been shut down or in remote fields where mile-long flowlines present their own challenges. Using the SSU for processed water is excellent for developing marginal fields and keeping mature fields with declining production profitable. The SSU can be used as a separation module, where oil as well as undesirable solids are removed from the water before it is reinjected or released back into the ocean.
In addition to applications in mature and marginal fields, SSUs work well with extensive well-testing as opposed to today's costly burn-off strategy. Finally, and perhaps the most interesting perspective for the future, NOV's SSUs eliminate the need for topside storage structures making them a vital part of oil production in extreme environments such as the Barents Sea, where permanent, manned surface structures are difficult to maintain due to distance and weather. Plus, surface structures go a long way towards bringing down oilfield operators' carbon footprint.
The SSU is part of a greater strategy by NOV's Subsea Production Systems (SPS) business unit. Spearheaded by the Flexibles Group and bolstered by the acquisition of Seabox™ subsea water treatment unit and Kongsberg's Subsea Products, NOV pursues a goal of innovating and simplifying subsea infrastructure and seeks to energize subsea oil production by reducing CAPEX and ensuring production growth.
By safely moving processing equipment to the seabed, operators can act on field intelligence as they receive it as opposed to having to plan everything in advance, which results in having equipment on FPSOs which must be maintained for years before seeing use.