Introduction

There are over 600 offshore oil and gas installations in the North Sea, 470 of which are in UK waters. These include sub-sea equipment fixed to the ocean floor as well as platforms ranging from the smaller structures in the Southern North Sea (similar in size to Big Ben) to the enormous concrete or steel structures as big as the Eiffel Tower and much heavier in the Northern North Sea.

Offshore there are also more than 10,000km of pipelines, circa 5,000 wells and accumulations of drill cuttings. Associated with these operations are also 15 onshore terminals.

Many of these structures have been producing oil and gas for almost forty years and are now coming to the end of their lifespan for which they were designed. Over the next couple of decades or so a growing number of redundant oil and gas installations will be taken out of service and decommissioned.

The industry needs to develop solutions to decommission these structures taking into account the impact on the environment, on the health and safety of workers involved, costs and technology required.

Under current regulatory requirements, over 90% of offshore structures will be completely removed from their marine sites and brought to shore for re-use, recycling or other disposal means. The rest which, comprises the very large and heavy steel or concrete installations (approx 10%), will be looked at on an individual basis to assess whether it is technically feasible (and safe) to remove them. If they are too difficult or dangerous to be removed to shore, an exceptional case for 'derogation' can be made.