Stolt salvages platform using mechanical cutting devices
J. Rouillon
Total E&P USA Inc.
Bob Starr
LoneStar Deepwater Consulting
Jay Stith
Stolt Offshore
Stolt Offshore has salvaged Total E&P USA Inc.'s Eugene Island block 275a production platform in the Gulf of Mexico using only mechanical cutting devices. The platform is located 70 mi off the Louisiana coast in 180 ft of water. Allan Palmer, general manager for regional projects and operations for Stolt Offshore in Houston, said the job required a combination of saturation diving and ROVs.
"Because of environmental and safety objectives, Total asked Stolt to conduct this major salvage operation without an arc being struck underwater, using remotely operated tools as much as possible," Palmer said. With the help of LoneStar Deepwater Consulting, Stolt Offshore conducted an extensive testing program to qualify the tools for the job. Some of the tools had to be redesigned and modified to work underwater. The testing and qualification period had to be completed quickly to begin salvage operations before the hurricane season.
In August 2002, Total was preparing the platform for abandonment. Original plans called for the removal of the deck for disposal onshore and the transportation of the jacket to a nearby artificial reef site. By October 2002, the production equipment had been decommissioned and P&A operations of the wells had been initiated.
At the same time, Stolt Offshore was contracted to abandon the pipelines leading from the platform. To accomplish this, the company sent its 210-ft saturation diving support vessel American Constitution to the platform site. Project Manager Jay Stith was in charge of the vessel when he received word that Hurricane Lili was approaching the Gulf of Mexico. As the hurricane, packing more than 120-mph winds, moved into the Gulf, Total and Stolt Offshore evacuated all personnel. By the time Lili reached the vicinity of Eugene Island block 275A, it had increased in strength to a Category 4 hurricane, carrying 140-mph winds.
"We were just completing work on one of the two pipeline P&As at the site when the hurricane struck," Stith said. "We waited onshore while oil companies carried out post-storm investigations."
By Oct. 4, 2002, the storm had passed. However, when Total returned to the area, they found the platform was gone from sight, Stith said. Because the P&A operation had already been completed, the loss of the platform did not create any pollution.
Assessing the damage
An ROV inspection of the platform indicated that the jacket had buckled 125 ft below sea level and had toppled to the west. The deck had broken free of the jacket and rested upright on the seabed.
This presented a different and more difficult set of problems for the project team. Broken jacket legs blocked safe access to the well area. The structural integrity of the deck and jacket was compromised.
Total asked LoneStar Deepwater, Stolt Offshore, and Noble Denton Consultants Inc. to provide a feasibility study and recommend options for mitigating the situation. Total was offered a menu of possible solutions that ranged from cleaning the entire sea bottom to removing only portions of the platform. The goal was to return the area to normal navigation status. It was also critical to avoid risk of future pollution while performing offshore operations respectful of the environment and minimizing risk to divers. Total worked closely with the appropriate regulatory agencies to ensure full compliance with all applicable environmental laws and permits.
For environmental as well as safety reasons, Total requested Stolt Offshore not use explosives. Many types of marine life, such as sea turtles and various kinds of fish, populate that area of the Gulf and might be injured by explosives.
Once Stolt Offshore performed a second ROV survey and confirmed the platform configuration, several possible solutions for the abandonment were presented. For each of the alternatives, the technical risks, the risks to divers, and the risks to the environment were assessed. The associated schedules and cost estimates were prepared.
After reviewing the options, Total elected to apply for a Special Artificial Reef Site permit to leave part of the platform on location. The company then chose a multi-staged solution comprising the following activities:
- Remove enough of the jacket structure to ensure a minimum clearance of 85 ft from the surface of the water for safe navigation purposes and safe access to the wells for final P&A
- Have the equipment that may still contain fuel or other hydrocarbons, such as compressors, generators and cranes, removed from the platform deck to avoid any future pollution
- Flood the remaining empty vessels on the deck to make them stable and prevent an uncontrolled ascent to surface
- Complete the plugging and abandonment operations of the remaining four wells in compliance with Total company rules to ensure a permanent leak-free abandonment
- Conduct a final survey to ensure all procedures were correctly implemented and all regulatory requirements satisfied.
Planning of the platform salvage operations began on May 15, 2003. The project was completed by mid-September.
The first step of the process was the testing and selection of remotely operated tools capable of severing 42-in. by 0.5-in. jacket legs with 39-in. by 0.75-in. grouted piles down to 8-in. diameter jacket members. Tools for stripping and cutting casings to get vertical access to the wells for further plugging were also tested.
"That was one of the most difficult parts of the job," Stith said. "We had to find heavy duty cutting tools that could be modified or redesigned to be used remotely while underwater. Before we took the tools offshore, we tested them at our Port of Iberia location at New Iberia, Louisiana."
Stolt divers participated in the tool testing to learn the intricacies of tool operations and to develop procedures for underwater operations.
These modified and redesigned cutting tools allowed Stolt Offshore to perform the first platform removal project done using only remote cutting devices, Stith said. The Stolt Offshore tool kit included heavy-duty shears and high-pressure abrasive cutters, diamond wire cutters, guillotine-type saws, and a variety of remotely operated mechanical cutters.
Some of the shears had never before been used underwater or in this particular application. Stolt Offshore adapted a travel cutter to make longitudinal cuts on the casing strings to prepare them for hot-tap operations.
"We adapted them for this situation," said Stith. 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.
The offshore operations began at the end of June with a thorough survey of the platform performed from the Seaway Defender. The objective was to gather all required information as necessary to perform the salvage works. During this phase, empty vessels located on the platform deck were flooded.
The salvage operations started on July 19. Stolt's derrick lay barge DLB 801 was the primary vessel for these operations. It was equipped with the company's Triton ST ROV, two smaller ROVs, and the SAT 11 portable diver saturation system. Approximately 150 employees worked around the clock to successfully complete the task. Stolt's Triton ST worked virtually non-stop for 60 days, with negligible downtime.
The 900-ton main crane and the deck crawler crane were used to deploy the cutting tools and to recover the severed jacket members and well casings.
"There was a lot of stored energy in the various wells and members to be cut," Stith said. "You have to be particularly careful when cutting pipe that is bent and twisted, to ensure divers' safety."
Noble Denton Consultants Inc. assessed 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 helps explain how the top sections of jacket legs were supported and, consequently, helped optimize the cutting sequence of the legs.
Stolt Offshore's Port of Iberia and Fourchon, Louisiana, offices handled the logistical portion of the project, with Bruce Edwards as manager of the offshore dive operations. Glen Lanier and Barry White acted as the DLB 801 barge superintendent.
The success of the project was the result of combined efforts by Total, LoneStar Deepwater Consulting, and Stolt Offshore. At the start of the project the objectives were clearly defined: Perform safe and environmentally friendly operations, meet or exceed statutory requirements. The use of remotely operated tools and compliance with Total rules for the plugging of wells facilitated these goals.
