JACK UP RIG
A jack-up rig is a type of drilling rig used at offshore locations. It is made up of a barge (or hull) and legs that can be lowered or raised onto the seafloor which will provide support for the main parts of the rig. There are different classes of drilling rigs and the jack-up rig belongs to the class known as Mobile Offshore Drilling Unit (MODU).
The use of MODUs is mainly for offshore locations for the exploration of hydrocarbons. And the jack-up rig is one of the most popular among the mobile offshore drilling units. They are also the preferred drilling rig choice for shallow waters (i.e 300 ft) to somewhat deep waters (about 550 ft).
When an offshore location is determined, the jack-up rig is then moved to that location. The legs of the rig are raised above the water and the barge section is allowed to float freely. At the proposed drilling location, the rig legs are then lowered onto the seafloor.
Understanding the Jack-up Rig
The term “jack-up” comes from the process of rig mobilization. When the rig legs are raised during movement, it is said to be in a “jack-up” position. While when the legs are lowered, the rig is said to be in a “jack down” position.
Most jack-up rigs have 3 legs, however, there are jack-up rigs consisting of 4, 6 or 8 legs. The barge of the jack-up rig also has holes that allow the legs of the rig to be raised or lowered as required. There are two types of elevating devices used in jack-up rigs that enable the up and down movement of the rig. They are the hydraulic cylinders and the rack.
TYPES OF JACK-UP RIGS
The types of jack-up rigs that exist are based on how they rest on the seafloor. There are two types of jack-up rigs: the independent-legged jack-up and the mat-supported jack-up.
The independent-legged jack-up rigs have cylindrically shaped steel shoes with pointed ends known as spud cans. The pointed ends of the spud cans drive into the ocean floor to give support and rig stability.
The mat-supported jack-up rig attaches an A-shaped steel shoe to the bottom of the legs. The legs rest firmly on the seafloor rather than penetrating the seafloor as is the case of the independent-legged jack-up rig.