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 how it removes old structures.
That backlog has passed but the need for more efficient methods remains strong for Chevron, and the industry, 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 include new approaches such as lifting whole structures 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; and now it is testing 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 the rig into pieces and lift the pieces out. The death of a diver when trapped gases from cuttings exploded was a powerful reminder that diving has always been one of the most hazardous jobs associated with removals, he said.
Seeking a way to reduce dive time associated with decommissioning, Chevron partnered with the maker of an enormous floating crane, Versabar Lifting Specialists, to develop a system for using the arch-shaped device to lift retired cranes out in a single piece.
The risk and cost associated with removing toppled platforms were higher, and hurricane damage magnified the uncertainties associated with removing old structures. The cost is generally about seven times higher, Stelling said.
Chevron worked with Versabar to demonstrate it could do the job, picking up a structure after it had been 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 that 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 1,400 hours or more to about 100 hours, Stelling said. It has adopted a device to shear metal parts, rather than use a torch, and will use remotely operated vehicles 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 hack saw. In April, the device cut a steel caisson 15 ft below the mudline in 12 hours, said Jon Khachaturian, president and chief executive officer of Versabar.
That avoided 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 was mud proved to be tougher to cut than steel, requiring seven hours compared with five for cutting steel.
Another innovation coming soon will be the splash diving boat, which is now under construction for delivery later this summer. The most notable feature of the vessel from Aqueos 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 with a system developed by the US military that sends a warning sound in multiple languages that can be heard more than 1,000 yards away to boats that do not respond to radio calls.
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 getting it ready for what comes next. “There is technology developed in the Gulf of Mexico that we will use around the world,” Stelling said.
