Three oilfield services firms collaborate on Murchison decom project

A specialist engineering firm, STATS Group, in collaboration with Paradigm Flow Services and Halliburton, isolated, de-oiled, plugged and abandoned two 3.5” subsea flowlines as part of the Murchison decommissioning project located in the North Sea. 

After nearly 30 years of operation in the Northern North Sea, the CNR International-operated Murchison field had reached the end of its production life.

STATS explained that, prior to the removal of the topsides jacket, it became evident that two subsea flowlines were still connected to the platform and these lines were known to still contain hydrocarbons and required to be de-oiled and cut to enable the heavy lift scope.

Aberdeenshire-based STATS Group was initially approached to review the requirement for subsea hot tapping operations but following collaborative discussions with Paradigm Flow Services and Halliburton, an alternative solution that would mitigate a diver-intensive operation was proposed that could be completed solely from the platform topsides, STATS said.

Initial discussions on the scope began in late 2013, and each element of the project was explored, developed and risk accessed. In May 2014, CNRI progressed with the platform-based solution and the contract was awarded.

In order to de-oil and abandon the subsea flowlines, full bore access was required in order to install Paradigm’s Flexi-Coil technology prior to pumping Halliburton’s Thermatek fluid system. The company said that, as there was no suitable valves to offer a positive isolation or provide an access point to gain entry to the flowline, STATS utilized its hot tap installed BISEP isolation tool.

STATS provided mechanical tie-in clamps, ball valves and a hot tap machine which allowed the flowlines to be hot tapped (drilled) while under pressure, allowing access to deploy the BISEP from a pressure competent launcher.

Once deployed, the BISEP was hydraulically activated setting the dual elastomer seals isolating the flowline. The seal annulus was then monitored and vented, independently testing both seals with full line pressure, the company said.

With the flowline isolated and vented from the platform behind the BISEP the line was cut, STATS then installed a mechanical connector and temporary launcher system, providing the full bore access required to deploy Paradigm’s Flexi-Coil technology.

The Flexi-Coil was initially used to de-oil the flowline but subsequently acted as a conduit to pump Halliburton’s Thermatek fluid system through the line.

The isolation, de-oiling and plugging of the two 3.5” unpiggable flowlines was completed and allowed the platform decommissioning to progress, STATS concluded.

Dale Millward, Director of EPRS and Subsea Services for STATS Group, said, “As a result of this collaborative project, the industry now has, where the field layout allows, a practical and cost-effective topsides solution for the isolation and abandonment of live or contaminated subsea flowlines. Unlike traditional techniques, this approach does not require a subsea intervention, eliminating the requirement for costly Diving Support Vessel or Work-class ROV vessels.

“The level of cooperation between all companies demonstrates the value of collaborative working to deliver solutions that would normally be out with any individual company’s capability.”