Offshore decommissioning of oil and gas facilities becomes necessary when the useful life of the structures, or when the fields that they tap into, have reached their limits. Oil and gas offshore platforms can be a considerable distance from the nearest onshore facilities equipped to deal with the task of decommissioning, so the task can be a difficult one.
In the North Sea, most of the oil and gas offshore installations have been in place for many decades. This means many of the structures are nearing the end of their useful lives and will need to undergo offshore decommissioning.
Offshore decommissioning is not a particularly easy task. In the North Sea this is especially so. The harsh conditions faced there raise their own special problems that have to be overcome. Removing huge installations from the sea bed where they have lain for several decades requires a lot of careful planning. This activity may also have an impact on the environment and the health and safety aspect for workers is another factor to be taken into consideration; while the cost of it all is likely to be enormous.
What happens when decommissioning takes place?
A plan of action is first put forward by the Operator who will carry out the dismantling of the structure. This needs to be approved by the government before any action can be taken. Once approval is given, the job can start. It will take a number of years and will involve many different organisations, each one responsible for a part of the whole.
Many service providers get involved in a project like this, in particular, companies with speciality skills in water jetting, cleaning, waste management, asbestos removal and so on. All the waste from such an operation has to be removed and disposed of and this is strictly regulated. They provide project management and technical support, cleaning and/or decontamination consultation, hazard identification, waste management (identification, removal, treatment, handling and disposal), asbestos management (identification, removal, handling and disposal), cold cutting of steel, concrete and other composite materials using water jetting, wire and mechanical methods. Upon CoP (cessation of production) they may carry out preparation for topsides removal and NUI (normally unattended installation). All the waste from such an operation has to be removed and disposed of and this is strictly regulated.
Despite human ingenuity in getting rigs up and running in the North Sea, it must not be assumed that any difficulties encountered in decommissioning them can easily be overcome. New technologies are emerging all the time to deal with problems that seemed insurmountable just a short time ago. Many of the structures can be floated away to a mainland base where decommissioning can be undertaken more easily. Those structures that cannot be floated away can, in most cases, be cut into smaller sections. The sections can be placed on barges and towed to land where possible. Where this is not possible, offshore decommissioning takes place where the installations lie.
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