End-to-end management and careful planning deliver safe and cost-effective platform abandonment in the Gulf of Mexico
Hurricanes Katrina and Rita left a trail of destruction as they raged through the southern part of the USA in August and September 2005; before making landfall, they had already wreaked havoc among the oilfields of the Gulf of Mexico.
The damage suffered by one small independent oil company’s facilities in the East Cameron field is typical of the problems faced by numerous operators. The facilities originally comprised two bridgelinked platforms: one dedicated to production and accommodation, and the other to supporting the wellheads. The former managed to survive both hurricanes. However, the wellhead platform was overturned by the second hurricane, Rita, and deposited on the seabed 45 m below the waterline.
Although the production and accommodation platform survived in sound condition and there was no pressure from the authorities, the operator felt, in 2008, that it was the right decision to reduce any future liability and remove the platform.
“The operator was looking for a third-party project management company to take on the abandonment work, one that had not only the necessary technical skills and experience but also a good understanding of the regulatory requirements,” says Tom Kennedy, president of InterAct. “Naturally, they also wanted the work done safely and in the most cost-effective manner.
“I believe that the operator’s decision to go with InterAct for this project was based on the ideas we put forward to reduce the cost of the project, particularly those for minimising expensive vessel time, our attention to detail and our determination from the outset to ensure an efficient offshore operation.”
The process, which closely followed InterAct’s proposed plan, involved abandoning the platform in stages. First, the topsides was decommissioned: a crew was mobilised to clean out all the production vessels, piping and so forth, and to sever any connections between the topsides and the jacket. Some of the heavier deck packages, such as the living quarters and the main compressor, were also isolated. There then followed a short, intense period when, with the help of a derrick barge, the topside packages were transferred in a series of lifts to a waiting materials barge.
InterAct’s plans for the jacket were to reef it on location in 50 m of water. This was by far the most cost-effective solution, and Kennedy’s environmental specialists prepared the necessary application to the Minerals Management Service (MM S). The positive response from the MM S was conditional on the jacket being placed on the seabed in a tightly specified position and orientation. Given the water depth and the weight of the jacket, and also the fact that the surrounding seabed was littered with debris from the earlier destruction of the wellhead platform, the MMS’s requirements rendered the whole operation far from straightforward.
Kennedy points out that any structure abandoned on the seabed in the Gulf of Mexico has to be at least 27 m beneath the surface of the ocean. This meant that it was necessary to cut the jacket in two, move the upper section and then topple it in a controlled manner.
Divers used diamond wire saws to sever the jacket legs and bracings, which had been pre-cleaned; the bottom section was left in place with the required 27 m of clear water above it. The upper section was carefully lifted off and placed upright 50 m away at the prescribed reefing site. “Toppling the upper section of the jacket to get it to land in exactly the right spot took great care,” explains Kennedy. “We undertook a thorough survey of the seabed using sonar to ensure there was no debris cluttering the site before attaching a line at the bottom of the structure and using the derrick barge to slowly tip it over. InterAct is one of only a handful of companies worldwide with experience of this kind of exercise.”
Once the operation was complete, InterAct surveyed both sections of the jacket and provided the proof required by the MMS that all of the abandonment conditions had been met. Kennedy reckons that the keys to the success of the project, from the operational and economic standpoints, were a good strategy and good planning, which minimised the marine equipment needs (for a start, a project like this would normally have required a much larger derrick barge) and the length of time the equipment spread was required on-site. In fact, it has been estimated that the project was completed for about $700,000 less than the existing benchmark cost for this kind of work.
“Platform decommissioning and abandonment is like any other offshore activity: you need to be creative,” says Kennedy. “There is always scope for saving time and money. It just requires you to take a fresh view of each project and then, most importantly, you plan the work meticulously.”