Offshore Jackup Drill Rig Infos.
Offshore jackup drill rigs are used as exploration drilling platforms, for offshore oil and gas platforms and offshore wind farm maintenance platforms. Offshore Jackup rigs have been widely well-known and many different kinds of offshore rig forms are in use.
The jack-up drill rigs are so called because they are self-elevating with three, four, six and even eight variable legs that can be stretched out i.e., jacked over or under the hull. The jackup oil rigs are towed by tug boats or transported by heavy lift ships or self propelled to the location with the hull floating on the sea surface while the legs stand up on top of the hull.
A self elevating offshore vessel or jackup drill rig is a form of transferable offshore platform that consists of a floating hull with an arrangement of number of changeable legs, competent of lifting its hull above the sea level. The floating hull facilitates shipping of the drilling rig and the entire necessary system to a required position. On the desired location the hull is lifted up to the required elevation above the water level by the support of legs standing on the sea floor.
Generally, jackup rigs are not self propelled and depends on powerful tug boats for tow or on giant float-on/float-off heavy load carriers for transportation. The legs of jackup drill rigs may be so constructed that it can pierce the ocean floor, may be built-in with inflated segments or footholds, or may be joined to an underneath mat.
When the offshore jackup drill rig arrives the designated location, the rig crew jacks the legs below through the water onto the sea bed with mat sustaining jackups or penetrates into the sea bed. This secures the Jackup rig and retains the hull suitably over the sea water. The hull is in fact a waterproof barge that sails on the sea level.
Offshore jackup rig is a barge fitted with long hold up legs that can be lift up or dropped down. The jackup rigs usually are without engine and towed by tug boats, or carried by heavy lift ships or may be also self propelled which is shipped into the work site with its legs raised and the hull sailing on the sea water. After reaching at the project position, the legs are jacked below onto the seabed.
Then process of preloading is done, where the load of the barge and extra ballast water are used to enter the jack-up rig legs firmly into the sea floor in such a way so that they will not pierce more into sea bed once the operations are commenced. After preloading, the jacking arrangement is used to lift up the whole barge on top of the water to a preplanned height or air gap, so that wave, tidal and current loading effects only on the relatively metal legs rather than on the vessel hull. Currently, jacking techniques use a rack and pinion gear assembly where the pinion gears are driven by hydraulic or electric motors and the rack is attached to the legs.
Relatively, jackup drilling rigs are used in shallow waters, usually less than 120 metres i.e, 390 feet of water. Though, an exclusive class of jackup rigs recognized as premium or ultra-premium jackups are known to have operational capacity in water depths reaching from 150 to 190 meters or 500 to 625 feet.
Different categories of jack-up rigs:
Mobile offshore Drilling Units-MODU: This kind of Mobile offshore Drilling rig is generally used in connection with oil and natural gas drilling. In mobile offshore drilling rig fleet, jackup drill rig types are mostly used throughout the offshore world. Other kinds of offshore drill rigs are semi-submersibles which float on pontoon like construction and drill ships, which are ship shaped vessels with rigs set up in their middle. In the drillship’s hull, there is an opening known as moon-pool through which these rig drills. Drilling tools required for drilling operation are passed through these holes. Also divers or ROV goes into sea through these opening.
Specialized Jackup Barge Rigs: Specialized barges are also refer to as jackup rig which are similar to an oil and gas platform but are utilised as a base for maintenance of other structures like long bridges, offshore wind turbines and drilling platforms. Jackup barge rigs may also be used to dismantle ship wrecked at sea.
Turbine Installation Vessel-TIV: The Turbine Installation Vessel-TIV rigs are usually used for installation of offshore wind turbine.
