BY KIS SØEGAARD
Substantial volumes of oil and gas remain in the subsurface of the Danish North Sea, but recovering them is technically complex and requires work above and below water.
Dan Bravo Rationalisation - a challenging three-year project that has reached its midway point – is an example of the complex subsurface and diving work regularly carried out by Maersk Oil’s Danish Business Unit. The project, which will rebuild Maersk Oil’s first-producing platform, Dan Bravo, also involves the conversion of the manned platform into an unmanned platform and is the first of its kind in the Danish North Sea.
The diving work with its challenging subsea removal and installation is an important part of the project.
“It is an example of the technically complex work that Maersk Oil, as the mature field operator in the Danish North Sea, is taking on to chase the barrels,” says Mark Wallace, Managing Director of Maersk Oil Danish Business Unit.
“When it is finished in 2015, it will have rejuvenated a complex that dates from 1972. The overall aim of the project is to extend the life of an already old platform to 2042. Giving it a lifetime of 70 years would be an achievement we can be proud of,” he adds.
Diving work in connection with Dan Bravo rationalisation is one example of the extensive underwater activity requrired in a mature field operation. Divers are working up to 40 metres below sea level. Maersk Oil carries out diving inspection on platform jackets bi-anually. 81 days are expected to be spent on diving in 2014.
Sizing up the job
Subsea work on the Dan Bravo Rationalisation began in 2013 with divers using photogrammetry – the process of obtaining measurements from photographs – to get accurate data on the dimensions for reinforcement clamps and a new conductor level for the Dan A platform.
“The structure is very complex, not least because it has been extended over the years as more oil and gas were discovered. We needed detailed information in order to fabricate to the most stringent requirements and photogrammetry was the ideal technology for this,” explains Project Manager Jakob Knudsen.
Fitted aboard a remote operating vehicle – which the team refers to as an “underwater flying saucer” – a special camera took thousands of images of the platform’s structure. These photos were then converted, using a software program, into 3D images. In turn, the images were used to develop detailed designs for the conductor level and clamps, ready for installation this summer.
This year’s diving work began in mid-April and the first of two stages was completed in July.
“The majority of the work has been on the Dan A platform, which has challenges with respect to fatigue. Back in the 1970s when it was built, people were not as familiar with fatigue as they are now and as our knowledge has grown we have developed innovative technical solutions to extend the lifetime of production from the field,” explains Knudsen.
Working below the waves
Divers have been working to a depth of some 20 metres, two at a time, from a diving support vessel. Using oxy arc and diamond wire cutting equipment, they have been removing Platform A’s existing conductor guide levels. They will then install clamps to preserve the structural integrity of the platform and the new conductor level. In total, 110 tonnes of reinforced metal will be used to reinforce the platform. Finally, the divers will fit a new boat landing to Dan B.
The second stage of the 2014 campaign began at the end of July with divers working at greater depths of up to 40 metres.
“We are more than half way through the diving work on the Dan Bravo Rationalisation and all parties involved – designer, fabricator, diving contractors and the project team - have out-performed expectations, especially given we are doing work that has not been done before and up to 40 metres below the surface,” says Knudsen.