Feature 3 | DECK AND HYDRAULIC EQUIPMENT

Innovative anchor concept for deepwater operations

Norwegian technology developers Deep Sea Anchors has recently received qualification for its Deep Penetrating Anchor (DPA) concept. Offering a more cost-effective alternative to anchors currently available, the DPA is set to take the offshore market by storm.

‘Dyptvann’ or ‘Deep water’ and focused the attention on mooring and anchoring. Tis was a reaction to the offshore market’s need for cost-effective solutions as oil companies move into deeper and deeper waters. Te council stipulated that the new anchor solution must be simple to install; the anchor cannot be complicated or too expensive to fabricate; it must have a holding capacity of at least 400-500tonnes for short-term loads and 300tonnes for long-term static tension loads, and the anchoring solution should allow for taut leg mooring and vertical pullout loading. DPA is a 13m loa, 80tonnes, ‘giant

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arrow-shaped’ anchor that is currently being tested as a mooring concept for offshore installations. Entrepreneur Jon Tore Lieng of Deep Sea Anchors is the brains behind DPA. Having worked as a geotechnologist with independent research organisation SINTEF, Lieng envisaged a more effective solution than box-like suction anchors of the time that were placed on the seabed. Box-like suction anchors are open at the

bottom and function by pumping out the water inside; thereby creating a vacuum that pulls the anchor into the substrate and acts as a permanent fixture. However, the need to precisely orient this type of anchor and its sensitivity to high seas and waves can contribute to problems when they are being deployed, and in many cases cause delays that can cost millions per day. For permanent mooring of floating

production storage and offloading units (FPSOs) and similar floating structures the practical alternative to DPA is the use of suction anchors, but they will normally be heavier and more difficult to bring through the splash zone. In addition, they must be oriented within +/-5 degrees in the direction

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his concept started as a research project initiated by the Norwegian Research Council in 1995 called

Deep Penetration Anchors on the main deck of MS Island Vanguard (Credit: Deep Sea Anchors/Island Offshore).

size and soil conditions. DPA on the other hand is simply dropped without the need for orientation or any suction operation. Lieng thought that the simplest concept

would be to drop a sufficiently heavy anchor straight down into the sea. If it was heavy enough and moving fast enough, such an anchor would force its way into the seabed and create a powerful hold. Two of the DPA have been installed

on Statoil’s (formerly StatoilHydro) Gjøa field near the Troll field in the Norwegian segment of the North Sea. The anchors, which were manufactured in Lithuania and were approved by Det Norske Veritas (DNV) in the last quarter of 2009, penetrate 31m and 42m respectively into the seabed. Te anchors are not affected by waves, and

Deep Sea Anchors new anchor concept. This image gives an idea of the size of the anchor (Credit: Deep Sea Anchors).

of the load, self-penetrate in a controlled fashion without too much tilt and then suction is applied (pumping water out of the anchor chamber) in order to penetrate fully. Te last part of this operation can take up to 6 hours, or even longer, depending on the anchor

the installation process does not change if the anchors are deployed at depths of 500m or 3000m. Each anchor is deployed under cable control until the final 75m of its journey where it drops in free fall until it reaches a speed of 100kts/hr. Te mooring line starts to pull taut when the anchor reaches the calculated penetration depth therefore there is no chain pile-up or damage to the mooring line. A remotely operated vehicle (ROV) follows the manoeuvre and transmits the

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