Types of oil and gas rigs
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The main types of Installation in offshore industry are:
Jack Up,Semi Submersible,FPSO, Fixed platforms, Steel Jacketed Platform, Concrete Gravity Platform, Floating Hotel (Flotel), Subsea wells
A Jack Up rig is a floating platform, which has legs attached to the side. These can be lowered to the seabed and then jack the platform out of the water. It can be either self propelled or towed to its location. For long distance “rig moves” heavy cargo ships are often used. Once in a position the legs are lowered to the seabed prior to starting drilling. The legs of the biggest platforms are as long as 120 m. Jack ups normally work in water depths up to 100 m, they rest on the sea bed and have an air gap (distance between water level and lowest structure deck) to stay clear of the high seas. The rigs are used for exploration drilling and are moved from field to field.
Semi-submersible, unlike the jack up a semi-submersible (often called as semi sub) is a floating drilling rig also known as MODU (Mobile Offshore Drilling Unit) the rig is supported with two large floats (similar to submarines). A ballast system allows the floats to sink to various depths and by this technique the floats are less affected by the wave motion of the sea giving it improved stability.
They are ideal for operations in rough or deep seas like the North Sea. Semi-subs are often self propelled. Once on location the MODU may use anchors to hold its position or it may have a Dynamic Positioning System or DPS to hold it in position maybe with the assistance of anchors. This allows the rigs to work in various water depths.
Steel Jacketed Platforms
Are of steel and can be very large with exploration rigs, some of them weigh over 100,000 tons.They are built onshore in different segments. Usually the supporting jacket, the legs of the platform that rest on the seabed, is built in one piece.When finished it is towed out by a barge and sunk into the production position.
The other elements of the platform (the accommodation, flare boom, drilling and production units, the utility plants, etc.) are built in segments and are placed on the top of the jacket by a crane barge. The process of putting the platform together and getting operational is called Hook-up. The process of connecting the platform’s production equipment to any pre drilled wells is called Tie - ins. When hook up and the tie ins are completed the platform can start to produce oil/gas. When oil/gas is produced there is often a considerable amount of unusable flammable gas and this is usually burned off via a long pipe called a Flare Boom. There at least 3 flare booms so the burned gas is not blowing onto the platform whatever the direction of the wind.
Concrete Gravity Platform
Built near the shore.On shore, the bottom or cells are built.Once finished, the floating cells are positioned in deep protected waters like a fjord (bay) when the rest of the platform will be built on the top in segments. The large structure will be towed out to its production location. As many as 10 strong tugboats are needed for the delicate maneuvers of the huge platform. When the platform is in position the structure is filled with ballast and sunk to the bottom. When the wells are activated and the hook up is completed, production can start. Pipelines are often used to carry the oil/gas to the shore for refining. The cells can be used to store oil in case the pipeline is damaged and cannot be used. This allows the platform to continue production for some days.
Floating Hotel ( Flotel)
Personnel for the hook up of the platform are based on a flotel (accommodation) connected to the platform under construction by means of a gangway. Very often jack up platforms are sometimes converted from production to hotel accommodation. Semi subs are also used. These are anchored or will stay alongside the platform using Dynamic Position.