SBS Energy Services (SBS) has completed a multi-phase project to decommission approximately 8.8 kilometres of insulated pipeline in the Gulf of Mexico in partnership with Helix Energy Solutions, setting a new offshore snubbing unit/hydraulic workover world record.
The project, which wrapped up in 22 days and ahead of schedule, consisted of retrieving and removing a pipeline end termination (PLET) to surface of a DP3 drilling intervention vessel.
The second objective was to use a 340K snubbing unit to rig up and intervene inside the pipeline with an optimised drill pipe string to perform washing/flushing operations until reaching the second PLET. A cap was then installed on the first end of the pipeline and placed back in the original trench on the seafloor with the deployment rigging and drill string for permanent abandonment in-situ. The final task was to record the final pipeline position on the seafloor.
A highlight of the operation was cleaning out the flowline rather than cutting it into sections. This approach significantly reduced the number of critical subsea lifts and overall timeline for the cleanout and lay down. Performing the full cleanout in a single lift also required minimal onshore disposal of flowline components, SBS explained.
This deepwater pipeline cleanout utilised the Helix Q4000, an intervention and construction vessel, working in 1000 metres of water.
Bobby Bray, president of SBS, stated:
“To our knowledge, this has never been done before, especially considering the total cleanout depth of almost 29,000 feet with over 25,000 feet of that being lateral length on the ocean floor.”
The highlight of the operation was to successfully trip in one time and trip out the drill string to the 8.77-kilometre actual drill pipe measurement; 1,000 metres water depth, 7.64 kilometres lateral and flush the pipeline. Another characteristic that makes this unique is that the pipeline lay on the sea floor is shallow versus a conventional well profile.
“Typically, interventions use the verticality of the upper portion of the wellbore, in this case the pipeline, to take advantage of gravity and the vertical drill pipe section to use the weight to lower the drill pipe string into the lateral,” explained Charles Overstreet, PE, president of Omicron Project Consulting, who provided the engineering design on the project.
The job also incorporated a special tool named “Crab Claw.” Crab Claw stores torque energy, while washing and rotating operations were ongoing.
“This was both a safety and an operational efficiency design. We stored the residual torque of pipe rotations while making up or breaking out subsequent joints. This saved measurable time and created a safer work environment,” added Overstreet.
To date, this is the longest subsea flowline cleanout operation via this method. The Q4000 also held a previous snubbing record depth of 7.25 kilometres set in 2006 during the Mariner Energy Pluto pipeline clean out.