Pipeline isolation in the Gulf of Mexico

There are no shortcuts when it comes to decommissioning and abandoning offshore production platforms. The process is time-consuming, costly, and involves meeting stringent regulatory requirements.

But what if offshore operators could reduce the risk of leaks when isolating the pipelines that feed into the platform? That would help them reduce environmental concerns, aid in regulatory compliance, and increase operational safety.

Those were the precise benefits Discovery Producer Services LLC, an American natural gas midstream service provider operated by Williams, realised when they decommissioned and abandoned a pipeline tied into production facilities in the South Timbalier area offshore Louisiana earlier this year. The project, located at a depth of 43 m (140 ft), included cutting and capping an 18 in. gathering line – part of a looped system being tied into another platform – without disrupting production.

As it would ultimately feed into another pipeline system, the 18 in. line was to remain pressurised and protected from seawater ingress throughout the cutting and capping operation. To accomplish these goals, Williams chose to isolate the line using STOPPLE® Train technology – a double block and bleed isolation system from pipeline service company T.D. Williamson. 

The STOPPLE Train isolation provides a number of benefits:

  • Reduced cost: fewer fittings, less time onsite, higher first-time success.
  • Reduced risk: fewer hot taps and welds (requires only one entry point).
  • Increased safety: two independent seals and bleed port.
  • Ensured environmental stewardship: no product release.

In contrast to traditional double block and bleed isolations requiring two hot taps and two fittings, the STOPPLE Train system provides two independent plugging seals inserted through a single hot tap entry – in this case, through a mechanical clamp and permanent ball valve. Less equipment affixed to a line and fewer tapped openings mean an exponential reduction in cost and risk, particularly when working with divers subsea.

To further reduce risk to personnel and the environment, this double block and bleed method utilises a bleed port between the two seals. The port captures any product that potentially escapes past the first seal, and removes it to a safe location away from the divers.

“This subsea isolation project was completed with no disruption to production,” says Randy Miley, TDW Gulf Coast Service Centre Manager. “Discovery’s job safety was enhanced and its environmental impact was brought to zero.”

Adapted from press release by Hannah Priestley-Eaton

Published on 17/06/2015

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