Submitted by Perenco
Impact
The immediate effect of taking the pipeline out of use was the loss of 60,000 barrels of water injection capacity per day on Furzey Island, ultimately leading to a loss of ~2,400 barrels of oil production per day.
The conventional Horizontal directional drilling option would have taken ~ 14 months to complete at a cost of ~ £5M. The deferred production during this period could be estimated to be over 1 million barrels of oil. In addition a new pipeline would require significant consultation and planning permission to drill in an environmentally sensitive area.
The selected ‘Pipe in pipe’ solution was completed in 6 months for a cost of £2.2M and a deferred production of 430 thousand barrels of oil.
Description of Best Practice
The Wytch Farm Oil field is situated in one of the UK’s most environmentally sensitive areas. On 9th March 2015 following a routine in-line inspection, a 1.2km section of 8” produced water pipeline connecting Furzey Island (in Poole Harbour) with F site (on the Goathorn Peninsula) was found to have severe internal corrosion. The pipeline was immediately taken out of service as a precaution to protect the environment and a project was initiated to restore production.
Conventionally the pipeline would have been decommissioned and replaced using a technique called ‘Horizontal directional drilling’. This would involve a significant project drilling a 1.2km borehole between the two remote sites. A new steel pipeline would then be constructed on the mainland and pulled through the new borehole. Finally the new pipeline would then need to be connected by welding into the buried pipelines at each site.
With technical support from Perenco’s head offices the local team looked for innovative solutions that could repair or re-use the existing pipeline. These included:
- A tight fit internal sleeve (pulling a PDFE liner into the pipe);
- A ‘cured in place’ pipeline liner; and
- A composite ‘Pipe in Pipe’ pulled through the existing 8” pipeline.
The selected ‘Pipe in Pipe’ solution involved pulling a 5”, 155 bar rated composite pipe through the existing pipeline using a small wireline unit on the mainland.
To restore the full 60,000 barrels of water to Furzey Island, an additional 5” and a 4” composite line were installed in two previously mothballed pipelines, already installed between Furzey Island and F site.
The material for each line came on one continuous reel, 1.3km long from the Supplier in Houston. These represented the longest continuous pulled through line of this diameter ever installed using this material. Importantly for the project team this meant that each line could be installed without the need for joints, and therefore potential leak paths in the carrier pipes under Poole harbour.
The actual pull through of each 1.2km line took less than 3 hours!
In addition, the project replaced significant sections of buried steel pipelines on both F & L sites. This involved several complex excavations up to 6m deep. The areas excavated are some of the most congested areas on site with many live pipelines, high voltage cables and other buried services. This required careful civil engineering design to maintain the excavations, to prevent interruptions to operations and to allow the pipeline team to install and weld the new pipeline in the excavations. In total 137 new welds were installed.
The work was successfully completed and the pipeline returned to service on 9th September delivering over 60,000 barrels of water per day to Furzey Island, exactly 6 months from the date the pipeline was taken out of use.
Contact: Rob Smith / Perenco UK
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