Types of Rigs that may Require Platform Decommissioning
There are a number of different types of oil and gas rigs. The removal of outdated or faulty rigs is known as platform decommissioning, which involves taking the rig apart, removing it from the site, and cutting up the pieces. Most rigs are situated offshore, many of them in the North Sea. Decommissioning a rig requires the expertise of skilled contractors, while there are many different rigs, the most common ones are a fixed platform rig, semi-submersiible platforms, jack-up and tension leg platforms.
The fixed platform is often the most common and usually the older type of rig. The platform is built on concrete or steel legs that are rooted into the seabed. The deck or platform contains the drilling rigs, quarters for the crew and also some facilities for production. The fixed rig is meant for extended use and could be standing for many years before anyone thinks about platform decommissioning. Fixed platforms are usually found in fields where the water is around 520metres deep.
Jack-up and tension leg platforms are used in different depths of water. As the name implies the jack-up platform can be jacked up above the surface of the water. The Jack-up platform is generally used in water that is 120metres deep, but depending on the size of the rig legs, could be up to 170metres. The jack-up rig is probably the easiest to move for platform decommissioning contractors because it is actually designed to be shifted from one place to another Tension leg platforms are generally platforms that are designed to float and upwards movement is prevented by the manner in which the platform is attached to the seabed Tension leg platforms are typically found in waters that may be up to 2000 metres deep. Tension leg platforms can pose a problem for the platform decommissioning contractor, largely due to the depth of water they need to work in.
The semi-submersible platform is erected on certain kinds of columns that are weighty enough to keep the rig in an upright position, but have sufficient buoyancy for the platform to float. Like the jack-up rig, the semi-submersible platform is designed to be shifted from one place to another. Sometimes ballast is used to shift the platform down or up and changing the buoyancy rate in the columns. When drilling and production are being carried out the rig is fixed to the seabed using a combination of wire and polyester rope and chains. Such rigs operate in depths between 60 and 3050 metres of water. Platform decommissioning contractors who may be required to remove the rig may find it easier than a fixed platform because it is designed to be moved.