A jack-up rig is a type of mobile platform that is able to stand still on the sea floor, resting on a number of supporting legs. The most popular design uses 3 independent legs, although in "mat-type" jackups the legs are connected to a hull.[1]
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The supporting columns may be moved up and down by a hydraulic or electrical system. During transit, the platform floats on its hull and is typically towed to a new location by offshore tugs. Some barge type rigs are self propelled. Then the whole rig is jacked up to an "air gap" elevation safely above the expected wave heights after the supporting legs reach the seafloor (perhaps penetrating many tens of feet to obtain solid footing in the case of independent-leg jackups). Jackup rigs provide platforms that are more stable than semisubmersible platforms but can only be placed in relatively shallow waters, generally less than 400 feet (120 m) of water.
A self-contained combination drilling rig and floating barge, fitted with long support legs that can be raised or lowered independently of each other. The jackup, as it is known informally, is towed onto location with its legs up and the barge section floating on the water. Upon arrival at the drilling location, the legs are jacked down onto the seafloor, preloaded to securely drive them into the seabottom, and then all three legs are jacked further down. Since the legs have been preloaded and will not penetrate the seafloor further, this jacking down of the legs has the effect of raising the jacking mechanism, which is attached to the barge and drilling package. In this manner, the entire barge and drilling structure are slowly raised above the water to a predetermined height above the water, so that wave, tidal and current loading acts only on the relatively small legs and not the bulky barge and drilling package.
This type of rig is commonly used in connection with oil and/or natural gas drilling. There are more jackup rigs in the worldwide offshore rig fleet than any other type of mobile offshore drilling rig. Other types of offshore rigs include semi-submersibles (which float on pontoon-like structures) and drillships, which are ship-shape vessels with rigs mounted in the centers. These rigs drill through holes in the drillship hulls, known as moon pools.
Jackup rigs also refer to specialized barges that are similar to an oil and gas platform but are used as a base for servicing other structures such as offshore wind turbines, long bridges, and drilling platforms.
 Jackup barges being used to dismantle a ship that was wrecked at sea. |
 Jackup barge servicing a Vestas V80-2MW wind turbine of the Scroby Sands wind farm. |
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