Allan Palmer, Stolt's regional manager of regional projects and operations in Houston, described the unique considerations of this salvage project.
"Because of environmental and safety objectives, TOTAL E&P USA asked Stolt to conduct the salvage operation without an arc being struck under water, using remotely operated tools as much as possible," Palmer said., "At the request of TOTAL E&P USA, and assisted by LoneStar Deepwater Consulting, we conducted an extensive testing program to qualify the tools for this job."
Stolt Offshore located heavy duty cutting tools that could be modified or redesigned to be used remotely underwater. Before taking the tools offshore, the company tested them at its Port of Iberia location at New Iberia, Louisiana. The remotely operated tools had to be able to sever 42" x 0.5" jacket legs with 39" x 0.75" grouted piles down to 8-inch diameter jacket members. Stolt also tested tools for stripping and cutting casings to get vertical access to the wells for further plugging.
These modified and redesigned cutting tools allowed Stolt Offshore to perform the first platform removal project done using only remote cutting devices. The Stolt Offshore tool kit included
One of the hydraulic shears used for the job produces 750,000 psi of cutting force. It had originally been designed to cut concrete piles and was modified for this big underwater project, Palmer said.
The abandonment project began in August 2002, with original plans calling for the removal of the deck for disposal onshore and the transportation of the jacket to a nearby artificial reef site. In parallel, Stolt Offshore had commenced abandonment procedures of pipelines leading from the platform. Stolt Offshore was managing the company's 210-foot saturation diving support vessel, American Constitution, at the platform site when Hurricane Lili approached the Gulf packing more than 120 mph winds. As the hurricane moved into the Gulf, TOTAL E&P USA, INC. as well as Stolt Offshore evacuated all their personnel. By the time Lili reached the vicinity of Eugene Island 275A in late September, it had grown into a Category 4 hurricane, carrying 140 mph winds.
By October 4, 2002, when TOTAL E&P USA, INC. returned to the area after the storm had passed, the platform had vanished. No pollution occurred, thanks to the decommissioning and abandonment already performed.
The platform jacket had buckled 125 feet below sea level and had toppled to the west. The deck had broken free of the jacket and rested upright on bottom. TOTAL E&P USA, INC. asked LoneStar Deepwater, Stolt Offshore, and Noble Denton Consultants, Inc. to provide a feasibility study and to recommend various ways to mitigate the situation. For environmental as well as safety reasons, TOTAL E&P USA, INC. requested Stolt Offshore not to use explosives. Many types of marine life, such as sea turtles, and various kinds of fish, populate that area of the Gulf.
After reviewing the options, TOTAL E&P USA, INC. elected to apply for a Special Artificial Reef Site (SARS) to leave part of the platform on location and then follow a multi-staged solution which included removing enough of the jacket structure to ensure a minimum clearance of 85 feet from the surface of the water for safe navigation purposes; removing equipment still possibly containing fuel or other hydrocarbons; flooding the remaining empty vessels on the deck to make them stable and to prevent them from making an uncontrolled ascent to the surface; and completing the plugging and abandonment operations of the remaining four wells.
The final step, just completed, was for Stolt Offshore to conduct a survey to ensure all procedures were correctly implemented and all regulatory requirements satisfied.
The salvage operations started on July 19, 2003. Stolt's derrick lay barge DLB 801 was the primary vessel for these operations. It was equipped with the company's remote operating vehicle, the Triton ST ROV, two smaller ROVs and the SAT 11 portable diver saturation system. Approximately 150 employees worked 24 hours a day, 7 days a week to successfully complete the task. Stolt's Triton ST worked virtually non-stop for 60 days, with negligible downtime. Stolt recorded 117 diving bell runs incident free.
The derrick lay barge's 900-ton main crane and deck crawler crane were used to deploy the cutting tools and to recover the severed jacket members and well casings.
Noble Denton Consultants, Inc. carried out an assessment of the residual plastic moment capacity at the bends in the jacket legs taking into account the extent of buckling through the leg section. This type of assessment helped explain how the top sections of jacket legs were supported and, consequently, helped optimize the cutting sequence of the legs.
"The project was completed in 60 days, a remarkable feat for the size and type of work involved," said Palmer. "We recovered almost 220 tons of steel, a dozen pieces of equipment and a box of wireline explosives left over during initial well abandonment operations – all safely and efficiently."
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