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Five landmark North Sea decommissioning campaigns

Lifecycle stage
Decommissioning

 

The fatigued conductor (left) and a Claxton tension ring  – part of the novel package Claxton developed to enable the recovery operation.

Claxton along with fellow Acteon company InterAct devised a strategy for P&A of the well (InterAct) and the recovery of the well conductors (Claxton) with a tight budget and time constraints in place.

Claxton designed and manufactured a bespoke conductor reaction recovery system that interfaced with the Leman platform. Comprising of support beams, hydraulic jacking system and Claxton’s positive grip tension ring technology to hold the conductor during recovery, the decommissioning also required the company’s full casing recovery package and SABRE™ abrasive cutting system.

Since this project, it has become widely accepted that operators can derive major cost efficiencies from rigless decommissioning and slot recovery operations. Following the completion of the Leman A1 projects, Claxton has been involved in more than 60 other North Sea platform well projects and has carried out of 280 cutting and recovery projects. Additionally, 75+ wells have been cut using the SABRE™ abrasive cutting system.

The methodology Claxton developed for Leman A1 has subsequently been used on multiple slot recovery, conductor recovery and well abandonment campaigns – enabling huge cost savings due to the rigless approach involved.

MAUREEN ALPHA

After producing more than 200 million bbl of oil between 1983 and 1999, Maureen Alpha was the first installation to be removed from the North Sea under OSPAR 98/3 – The Disposal of Disused Offshore Installations agreement.

Maureen Alpha being towed to dock after floatation. The entire operation called on multiple supply companies and enabled the development of new technology at the time – Claxton’s SABRE™ cutting system being just one example.

It was also the largest and heaviest non-concrete structure that was re-floated in the North Sea.

After owner Phillips planned (since 1993) and completed the 60-hour operation, the platform was lifted off the seabed by injecting water under the base while deballasting seawater in the structure’s three tanks. The decommissioning of Maureen was the catalyst for the development of Claxton’s SABRE™ abrasive cutting system – the tool was used for the first time during the decommissioning program.

The one-well satellite facility, Moira, was also removed as part of the project and safely recycled and disposed of onshore.

NORTHWEST HUTTON

The platform was the only integrated oil and gas drilling production process in the North Sea which also included an accommodation facility on the field too.

First discovered in 1975 by the Amoco Group, the field has a total estimated reserve of 487 million boe. Despite start production in 1983, the platform was closed by the UK Government 19 years later after reports found that no more reserves could be recovered from the field.

At the time of production ceasing in 2003, it had recovered 126 million boe.

The decommissioning started in 2006 and finished 3 years later, however reports by Fairfield’s engineers have revealed that the reserves could be tapped into once more.

Conductors on the Indefatigable field, just prior to cutting and recovery commencing.

INDEFATIGABLE FIELD

First discovered by the Amoco Group in 1966, the Indefatigable field lies in the Southern North Sea and initially started as a manned platform in 1977.

However, in the 1980s it converted to a ‘not normally manned’ facility and continued to supply reserves successfully for Shell, Esso and Perenco until 2005.

Consisting of 26 wells, 6 platforms and 5 pipelines, the field continued to be decommissioned until 2010 with 13,000 tonnes of equipment and steel removed and recycled onshore. Claxton provided abrasive cutting of the well conductors for the Indefatigable field, along with cut verification, conductor pinning and fitting high-load lifting flanges – this approach enabled the operator to recover the conductor strings later using a lift vessel.

BRENT SPA

A cornerstone of the UK’s oil and gas industry, the Brent oilfields and its platforms have come to the end of their life cycle. However, it was back in 1999 when Brent Spa was decommissioned that this became a landmark project.

Costing Shell at least £60 million on the operation, this project could be seen to set a precedent for the industry for onshore disposal.

Despite a public, media and government debate about deep water disposal in 1995, a year earlier the 66,000 ton structure was initially given approval for sinking. The issue was a topic raised at the Oslo and Paris Commissions in the same year which saw 11 states calls for a halt to all offshore sea disposals.

Following this, Shell moored Spa to shore before disposing of the structure in 1999.

LESSONS LEARNED

A 2014 survey by Oil & Gas UK found that a handful of large decommissioning projects are already well underway and more will be delivered in the next 5 to 7 years.

Experience gained from the above projects have helped to pave the way toward generating a more cost effective and efficient environment for operators. Nevertheless, close contact between the supply chain and industry will be essential for forthcoming decommissioning works, as new technology, and greater capacity will be needed in the coming decade.

Decom case study pack
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Decommissioning Case Study Pack

The Claxton offshore decommissioning case study pack showcases our vast experience of delivering successful decommissioning projects.

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