3 of the oldest mobile drilling rigs have been sent for scrapping, according to recent media reports. More old rigs are also mentioned as candidates for additional scrapping. This is probably not good news for the owners of these rigs or for the employment of crews, but they had all been laid up for some considerable time anyway.
These oldest rigs were originally built without the reserve buoyancy capability that was introduced after the Alexander Kielland accident in 1980, they were subsequently modified to provide this additional buoyancy capability, but with less robustness in an extreme accidental scenario. Those rigs that have this requirement as the design basis are significantly more robust, especially in an extreme accidental scenario.
When West Venture had a severe supply vessel collision in 2004, it was good that it occurred on a new semi-submersible unit, had it been one of the old rigs, it could have caused a column to break off, and in the worst case ended up with a scenario similar to the Kielland accident.
But all of these old rigs have performed well for several decades, actually, the reserve buoyancy introduced after the Kielland accident has only once worldwide been called for in the long time since 1980, with the severe flooding of BP’s Thunder Horse production semi in GoM in one of the storms in 2007, ten years ago. When the personnel returned from shore after the storm, they found the installation with severe listing due to water flooding, but floating on the reserve buoyancy volume in the deck structure, thus saving the installation from total loss, even before the production had commenced.
For the safety of employees on mobile units, it is an improvement that these oldest rigs are removed from the market place, even if they have been popular for some of the less demanding drilling operations for a long time.
Norway has an ambition to be world leading in offshore health, environment and safety. The scrapping of these old rigs will be an element in improving the safety of mobile units in Norway.