By Stephen Rassenfoss | 9 May 2014
A destructive run of three hurricanes has been a catalyst for a flurry of innovations in decommissioning shallow water wells in the US Gulf of Mexico. Faced with the costly job of removing more than 30 damaged platforms and other damaged structures, Chevron began a series of technology development partnerships that changed the way it removes old structures. That backlog has now been reduced, but the need for more efficient methods is still strong for Chevron and for the industry at large, which is faced with thousands of structures on the continental shelf for fields that are played out. The goal has been to “engineer out risk,” said Don Stelling, president of Chevron Environmental Management Co.
The changes included new approaches like lifting whole structures intact rather than cutting them up and removing them piece by piece, using a giant claw rather than cables, saving the many hours needed for a conventional lift. Now it is testing a method using an abrasive cable to saw off supports below the water line, further reducing diving time.
“The mission was to do it more safely, and it is more efficient,” Stelling said. “We are saving money and eliminating a lot of risk.”
When Chevron began removing its platforms demolished by hurricanes Katrina, Rita, and Gustav, the standard procedure for removing structures was for divers to cut rigs into pieces to be lifted out. However, when a diver died in an explosion of gases trapped by cutting, it was a powerful reminder that diving has always been one of the most hazardous jobs associated with removals, Stelling said.
Seeking a way to reduce the risk and dive time associated with decommissioning, Chevron partnered with the maker of a enormous floating crane, Versabar Lifting Specialists, to develop a system for using the company’s arch-shaped device to lift retired cranes out in a single piece.
The risks and cost associated with removing toppled platforms were higher. Hurricane damage magnified the uncertainties associated with removing old structures, and the cost is generally about seven times higher, Stelling said. Chevron worked with Versabar to demonstrate it could pick up a structure after it had cut from its moorings. That led to a continuing series of collaborations to improve the method and further reduce dive time.
The next step was the Claw, an apt description of the device that hangs from the top of the arch-shaped Versabar and is able to grab whole structures and lift them without the modifications needed to attach cables. For example, using the claw reduces time needed for lift from upwards of 1,400 hours to about out 100 hours, Stelling said. It has adopted a device to shear metal parts, rather than use a torch, and will use remotely operated vehicles (ROV) rather than divers when possible.
Now Versabar and Chevron are field testing a new device designed to cut the legs of platforms below the mudline using a long, abrasive tungsten carbide cable that is worked back and forth like a hacksaw. In April, the device cut a steel caisson 15 ft below the mudline in 12 hours, according to Versabar president and CEO Jon Khachaturian. That eliminated the many hours of dive time required to clear out the mud in a 90-ft circle around a caisson to provide divers access. One surprise from the test: mud proved to be tougher to cut than steel, requiring seven hours compared to five for cutting the steel.
Another method coming soon will be the Splash Diving Boat from Aqueos, which is now under construction for delivery later this summer. The most notable feature of the vessel is a power system that uses jets rather than propellers, allowing it to hold its position at dive sites where dropping an anchor could damage pipelines below. It is also designed to move faster, make it easier for divers to enter and leave the water, and warn encroaching boats away with a system developed by the US military that sends out a warning sound in multiple languages to boats that do not respond to radio calls. The alert can be heard more than 1,000 yards away.
The Gulf of Mexico has been a technology development center for Chevron Environmental Management, but its mandate is global, with projects in 35 countries. The large-scale decommissioning going on the Gulf of Mexico, where it has 450 structures to go, is helping the company prepare for what comes next. “There is technology developed in the Gulf of Mexico that we will use around the world,” Stelling said.
Stephen Rassenfoss is the Emerging Technology Senior Editor for the Journal of Petroleum Technology.
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