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Claxton and OIS improve decommissioning technology to deliver subsea well abandonment campaign

12th October 2015

Claxton has improved the technological advantage of its Suspended Well Abandonment Tool (SWATTM) by developing an extension module. In turn, this enables Claxton and Offshore Installation Services Ltd (OIS), to set deeper environmental and intermediate barriers.

Claxton's Suspended Well Abandonment Tool (SWATTM)
Claxton's Suspended Well Abandonment Tool (SWATTM)

Neil Watson, SWAT product leader, Claxton, said, “SWAT holds the Queen’s Award for Innovation in the UK, and the Petroleum Institute Platinum Award for Innovation. It is the first tool of its type, and is provided by Claxton in co-operation with OIS. In combining our proven SWAT tool with the new extension module, we have significantly increased the range of wells that can be abandoned using SWAT. By providing our customers with more opportunities to opt for this rigless method, we enable them to reduce their well abandonment costs considerably.”

The existing multi-award winning SWAT tool is deployed from a vessel of opportunity through the moonpool, eliminating the need for a drilling rig. It is positioned on the wellhead and then used to perform casing perforation, recovery of drilling mud and placement of the required cement barriers in the well.

SWAT utilises the extension module to enable cement to be positioned even deeper within the well. A wiper plug is positioned before and after the cement column, which ensures that the wellbore is cleaned ahead of the cement. The lower plug forms a base for the column and slurry is uncontaminated when it enters the annulus. The cement is then displaced to the required depth in the well. In OIS’s most recent well abandonment campaign, the depth was 2400 feet below mudline. This added depth capability significantly enhances well decommissioning capacity; previously, the SWAT tool was limited to environmental barriers up to 600 feet below mudline, which limited the wells eligible for abandonment with SWAT.

OIS successfully completed its 18th multi-operator plug and abandonment (P&A) campaign for Centrica Energy and Antrim Energy in the central North Sea, using Claxton’s new SWAT extension module. Ten subsea wells in categories 1, 2.1 and 2.2 were abandoned with the rigless method.

Valerio Percoco, vice-president business development, OIS, said, “This project is the largest well decommissioning campaign completed by OIS since Acteon sister company, Claxton, introduced SWAT in 1996. The successful completion of this project, with zero environmental or lost-time incidents, reinforces our position as a global leader in the vessel-based P&A market, having safely abandoned 128 wells over the past 19 years. Furthermore, this multi-operator approach enables operators to share project costs, which, when combined with the rigless approach, provides a cost-effective method for decommissioning non-revenue generating assets. Project costs are divided equally between operators on the basis of number of wells brought to the campaign, and lump sum costs such as mobilisation and demobilisation are shared.”

OIS conducted offshore operations from an anchor-handling tug supply vessel (AHTS) the Island Valiant. In phase one, Claxton’s SWAT system was deployed through the vessel’s moonpool to perforate, circulate and set cement barriers in the bore and across all the casing annuli. An AHTS is more cost-effective and fit for purpose than a construction vessel or rig; able to move quickly and easily between work site locations and conducting operations using dynamic positioning, which saves significant amounts of time compared to using a semi-submersible or jack-up/drilling rig. Intervention operational times are also reduced with a vessel, which are typically between 36 – 60 hours.


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