The Creation of the World’s Highest-Pressure Large-Bore Drilling Riser
An offshore riser is used to connect a subsea blowout preventer to a surface rig so that the mud churned up during drilling is vented to the surface instead of spilling out of the stack and onto the ocean floor. There are a number of different types of offshore risers, each with its own specific use and function. However, few offshore risers get the attention that the riser created for Venture Production did. That’s because this riser single handedly extends the operating envelope of Jack Up rigs into territory that was previously serviced by more expensive Semis.
This offshore riser, built by Acteon companies Subsea Riser Products and Claxton Engineering, is not like any other riser in the world. It’s the first full-bore access riser that can handle pressure over 12,000 psi. It was no easy task to design such huge !a href="http://www.claxtonengineering.com">drilling risers that can handle the pressures that Venture planned on putting on it. While creating a full-bore riser, which is 18 ¾ inches, is no problem, and creating a riser that can withstand 12,000 psi is likewise not a difficult task, creating an offshore riser that incorporates both was a great challenge. Part of the problem was that the sheer weight of such a riser would be incredible. It would also be difficult to attach connectors to the thick pipes that would be required, and even if connectors were attached, they would suffer from welding difficulty due to the known issues around welding high-grade steel.
Thus, an innovative approach was needed. Both are difficult to weld and work with. However, the plan the team came up with met requirements and avoided both of these difficult standard solutions. They shrink-fitted the flanges to the pipes, eliminating the need for welding at all. Shrink fitting is often used in other industries, but this was the first time it was applied to an offshore riser.
Once in place, the riser will be capable of drilling HP/HT subsea wells. It will be placed on a jack up drilling rig that uses a surface blowout preventer. This will result in a significant reduction in drilling costs versus the traditional approach of using a Semi Submersible rig for HP/HT drilling.
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David Bennet is an experienced engineer in the marine industry and has been specialising in drilling risers for more than 18 years.
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