As discussed yesterday, drilling forms part as one of the major activities within the oil & gas industry. There are 4 main types of drilling platforms and yesterday we kicked off with the jack up. Today I will elaborate on a semi-submersible as the blog topic for today.
Supported by vertical columns on submerged platforms and never entirely underwater, a semi-submersible drilling rig is usually a self-propelled working platform. Semi- submersible rigs make stable drilling platforms for offshore oil and gas activities and the component can be elevated or dropped in the water by shifting the amount of water weight on the platforms. The platforms used during operations are less influenced by any ocean disturbances the lower the platform is situated underneath the sea. By implementing this, vertical movement is decreased allowing continuous drilling in reasonably bumpy seas.
Invented by Bruce Collip, the design was initially established for offshore drilling purposes. With the capacity to hold up to 100 crew members on board, semi-submersibles can operate drilling in water depths up to 300 meters plus. With advancing technology some semi submersibles can drill in water depths over five thousand feet. 1961 saw the arrival of the first semi-submersible.
With the semi-submersible exterior structure underwater at a deep draft, the vessel is less influenced by wave action compared to normal vessels. Stability is critical and therefore it is important to remember that such vessels are sensitive to change in load. De-ballasting allows for the semi-submersible drilling platform to renovate from a deep to a shallow draft therefore transforming into a surface vessel. Up to 8 massive anchors have the duty of securing the position of the semi-submersible drilling platform. In order to keep the vessel motionless dynamic positioning (DP) mechanisms make use of computer controlled directional propellers.