Most offshore installations in the North Sea were built in the 1980s. The lifespan of a platform is 30-40 years and the legislation obliges the owner to dismantle these facilities when they are no longer in operation. Therefore “decommissioning” will become a common practice in the coming years and takes place according to the following steps: installation on the platform of a device sized for the abandonment of wells; abandonment of production wells;
dismantling of the main bridge; dismantling of the structure. For the first step, there is the question of rehabilitating the drilling rig still present on the platform or using another unit. For the Gaviota platform, it was decided to rehabilitate the existing drilling rig in order to carry out well maintenance operations. However, the problem would have been the same if it had been to stop and abandon the wells.
It will first be a general presentation of the “decommissioning” offshore platforms and problems to be solved and then an example of rehabilitation of a drilling rig on an offshore platform to make operations on wells.