Decommissioning Done Right

Friday, October 02, 2020

When it’s time to begin the process of decommissioning an offshore oil and gas platform, there are many factors to keep in mind. For example, the age and location of the structure, as well as its history and any unique features may need to be considered. And then there are always unknown potential hazards that may arise while work is underway. That is why effective preliminary planning, engineering and permitting are critical to ensuring a project is completed safely and on schedule. Though the work scopes and regulations governing decommissioning are widely known throughout the industry, each platform comes with its own specific challenges.

Planning depends upon several variables, including the year the platform was installed, its location, water depth, maintenance history, platform conditions and budget. All these factors must be taken into consideration in order to safely prep, disassemble and remove a facility. Given this complexity, it pays to have an experienced team in place who can creatively resolve any issues that arise.

Danos has assisted oil and gas producers with the decommissioning of platforms in the Gulf of Mexico for many years, providing a number of services including fabrication, construction, scaffolding and project management support. With years of experience working as a team across projects, Danos’ personnel are highly skilled and adept at managing complex operations with multiple service lines. Decommissioning is challenging work that requires both expertise and a well-coordinated and organized team.

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In 2018, Danos provided support for a major oil and gas producer’s two-year decommissioning project. According to a client project engineer, “Danos was a great partner on this project and provided innovative solutions while operating safely and efficiently."

The eight-leg fixed platform was located in the Gulf of Mexico in 350 feet of water. Though it had been cutting-edge when it was installed in the early 1990s, production had not met projections, and the owner was ready to abandon the facility. Having recently tried rigless plugging and abandonment (P&A) operations on similar platforms, the client opted for the higher cost, established methodof using a drilling rig on the platform. Fortunately, the original drilling rig was available, which eliminated a considerable amount of prep work. However, there were still several modifications needed to make sure the project could be completed safely.

One modification was the installation of a new power system. The original system had been dismantled when the facility was originally shuttered. In order to power the platform during the decommissioning campaign, Danos installed a new generator and fuel tank, along with the associated piping and safety systems. The platform also required the fabrication and installation of several new skid beams, along with other reinforcements to the existing structure. This allowed for a Seatrax 250 crane to be safely installed to support the abandonment work on the platform.

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As part of the project scope, Danos performed the air gapping, flushing and demolition of the existing production trains. This work required an extensive cutting and welding campaign that posed certain challenges. While the normal process for ensuring a safe operating environment is to conduct all work within a pressurized welding enclosure (PWE), in this case Danos had to find an innovative approach. Due to the proximity of the wellhead, in some cases only 10 feet away, Danos instead used the PWE to enclose the wellhead — rather than the cutting and welding work. This inversion allowed the team to monitor wellhead hazards while conducting the cutting and welding operations safely and efficiently.

Another major component of the work scope was prepping the platform for removal by the heavy lift contractor. Danos welded lifting eyes on piles and the platform and air-gapped the platform legs to allow for easy removal of the deck. The crew also assisted the abandonment contractor with cutting conductors, piles and jacket legs below the mud line.

Once this prep work was complete, the platform was removed via Versabar’s VB 10,000 heavy-lift vessel, outfitted with a spreader bar and slings that were secured to lifting eyes installed by Danos. Finally, the jacket was lifted and towed 30 milesand deposited on the seabed as part of the Rigs to Reefs program. An eight-leg structure like this one can typically provide a home for 12,000 to 14,000 fish, according to a study by the Coastal Marine Institute.

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After two years and more than 130,000 Danos man-hours, the platform decommissioning was complete and executed without incident. Thanks to an experienced team and multiple service lines working together seamlessly, Danos was able to play a vital role in the project’s success — working with the customer to support the decommissioning campaign each step of the way, from initial planning and prep to final lifting and removal.

“This project is a great example of what Danos does best: tackling complex challenges with a well-coordinated team of experienced professionals, all with no recordable incidents,” says James Callahan, VP of Project Services for Danos.