acoustic signal that releases the anchor for the final stage (75m) of the descent. Ten the ROV goes down to check the situation on the seabed, and the chain is tightened up. A typical mooring configuration for a

platform will consist of 12 to 16 anchors located in three or four groups. All the anchors can be carried by a single auxiliary vessel and deployed in the course of a single trip to the field.

Field testing

Getting to the current stage of full-scale trials has been a long path for Lieng. At the same time as the offshore industry was beginning to move to deeper waters in the 1980s, the Norwegian Research Council launched its deepwater and offshore programmes, which looked at proposals for new mooring technologies. During that time Lieng carried out a

theoretical study, which he sent to all of the oil companies based in Norway. His concept was initially turned down, but it gave him exposure and made the companies aware of this idea. In 1997, Lieng took his idea with him when

he leſt SINTEF and set up his own company, GeoProbing Technology, with a licence for the patent. Aſter a while, he made contact with people in Statoil who liked his ideas, and in 1998 and 1999 the company financed feasibility studies and model tests. Te idea was to find out how large the anchor needed to be, and perhaps more importantly how much it would cost. Te scientists soon worked out that the

new anchor concept would cost about 35% less than the technology then in use. Since operational costs can be in the region of hundreds of millions in Norwegian Kroner, this meant a significant saving. In mid-2003, Lieng and the Statoil

scientists moved into the Trondheimsford to test a 4m scaled-down version of the anchor. Te fibre cable attached to the anchor broke near the seabed when they were testing its holding power, and the anchor was lost. Lieng comments on that day: “As well as the anchor itself, all of the instrumentation was installed in its tail-end. Tat was a bad day.” Te anchor lay on the seabed for three

years before it was found again and another company took on the job of bringing it to the surface. Meanwhile, the project was abandoned, and Lieng worked as a consultant

Lifting the Deep Penetration Anchors to the moonpool (Credit: Deep Sea Anchors).

in offshore marine geotechnology. When probed by Offshore Marine

Technology as to the reasons behind the fibre rope breaking during the first operation, Lieng said: “Why the new and previously unused fibre rope that we [Deep Sea Anchors and Statoil] used for our test in Trondheimsford broke at ¼ of its presumed breaking load is still a mystery. Fibre rope is a necessity in order to reduce weight especially in deepwater fields. For large floating structures such as FPSOs the bottom part of the mooring line is a chain, then a length of fibre rope and then chain again through the marine growth and splash zone.”

Current situation

Following on from that low point, things began to move forwards again. Statoil is currently evaluating a number of development projects off the coast of Norway that involve

Offshore Marine Technology 2nd Quarter 2010

depths of around 1000m, as well as 30 or so deepwater fields in the Gulf of Mexico, all of them more than 2000m deep. Tese evaluations have brought the problem of cost-effective mooring back to the fore. Te Gjøa field is the first full-scale trial

being run by Statoil, and the concept is gradually gaining acceptance. Lieng adds that several oil companies are showing genuine interest and is hopeful that the concept will be acquired by other oil companies. Lieng is busy in the national and

international marketing phase, visiting field development operators, oil companies and offshore companies that supply mooring systems. Lieng added: “I am counting on making

us known as one of several possibilities, and I believe that we can make our mark in the competition to supply mooring system, in terms of both price and robustness.” OMT

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