Types of Rigs Needing Decommissioning Services
The process of removing an oil or gas rig that is no longer needed is known as decommissioning. There are different types of rigs and some of them are easier to cut up and remove than others. Many rigs are based offshore, typically in the North Sea and a lot of them have been there for decades. Older oil and gas rigs are rooted to the sea bed and have to be cut up before they are moved offshore. Newer rigs often have floating platforms, which means that they can be untied from the seabed and floated back to the mainland for decommissioning there. All decommissioning of rigs involves cutting them up and putting the pieces into safe storage until they are needed to build another rig. Most of the pieces have been in contact with noxious substances, which is treated like hazardous waste and so they have to be stored in a safe facility.
Fixed Rigs
The fixed oil or gas rig is generally the older type of rig built before the mid nineteen nineties. A fixed rig is one that is constructed on legs made of steel or concrete, which are then fixed or anchored directly into the seabed. On top of the legs is a deck or platform holding crew quarters, the drilling rigs and facilities for production. Fixed rigs are immobile because they were designed for long term use. Most fixed platforms work better in water depths up to 520 metres. Older rigs are often more difficult to decommission than more modern structures. Specialist decommissioning services are needed to dismantle fixed offshore rigs.
Jack-up Platforms
A jack-up rig is a platform that is designed to be jacked up above the surface of the water and has legs that can be lowered in the same way as jacks are lowered. A jack-up platform is usually located in water up to a depth of 120 metres, although some of the larger platforms of this type may be used in depths up to 170metres.
Semi-Submersible or Floating Platforms
Floating or semi-submersible platforms are those rigs that have columns that are buoyant enough for the platform to float on the surface of the water but with enough weight in them to ensure that the rig stays upright. Floating platforms are essentially structures that are designed to be moved from place to place, this type of platform is easier for decommissioning services because it can be moved before cutting. These platforms are kept in place by what is known as dynamic positioning or by the use of a mix of chains and wire or polyester rope. Floating platforms may operate in water depths of between 200 and 10,000 feet.