Types of drilling rigs

 Types of drilling rigs

The complexity of the drilling operation determines the level of sophistication of the various rig components. However, even with the considerable variety of rig types, the basic components described under with only a few exceptions are similar and

common to each.

Rigs are generally divided into two categories

1-Onshore

2- Offshore

Onshore (land) rigs are all similar, but offshore rigs are of five basic types - each of which is designed to suit specific offshore environment. Illustrates the various types of rigs. 

-Land Rigs

Before rig equipment is brought in, the land must be cleared and graded, and access roads must be prepared.

The most common arrangement for a land drilling rig is the cantilever mast (sometimes called a jackknife derrick) which is assembled on the ground  then raised to the vertical position using a power from the draw words (hoisting system).These structures are made up of prefabricated sections which are fastened together by large pins. First, the drilling crew places the engine and derrick substructures in proper position and Pinned together and then the draw works and engines are put in place

 

 

 

Offshore Rig

A-Barge

The barge is a shallow draft, flat-bottom vessel equipped as an offshore drilling unit, used

primarily in swampy areas. This rig can be found operating in the swamps of river deltas in Waste

Africa or in the coastal areas of shallow lakes such as Lake Marcaibo, Venezuela. It can be

towed to the location and then blasted to rest on the bottom

B-Jack-up

This mobile drilling rig is designed to operate in shallow water, generally less than 350 ft deep.

Jack-up rigs, are very stable drilling platforms because they rest on the seabed and are not

subjected to the heaving hull which may be shipshaped, triangular, rectangular, or irregularly

shaped,, supported on a number of lattice or tubular legs

When the rig is undertow to a drilling location the legs are raised, projecting only a few feet below

the deck, and the structure behaves like a cumbersome floating box; hence, it can be towed only in good seas and at a slow speed Upon reaching its location the legs are lowered by

electric or hydraulic jacks until they rest on the seabed and the deck is level, some 50 feet or more

above the waves. Most jack-up rigs have three; four or five legs are either vertical or slightly tilted

for better stability. In one design, they are fixed to a large steel mat, which gives it the name of matsupported jack-up. A drilling derrick is cantilevered over the side

The chief disadvantages of the jack-up are its vulnerability when being jacked up or relocated

but as a class, they are cheaper than other mobile rigs. Nearly half of the world's fleet of offshore

rigs in service is the jack-up type, some of which are large, self-propelled Units

 

C-Fixed Platforms

There are two basic types of fixed platforms are

"pilled" steel platforms and "gravity structure".

Both types discussed below.

Pi led Steel platforms

These are conventional drilling and production platforms, and hundreds of them are installed

offshore in many parts of the worlds. The standard configuration consists of a steal jacket

pinned to the seabed by long steel piles, surmounted by a steel jack deck with supports

equipment and accommodation buildings or modules, one or more drilling rigs, and a

helicopter deck. Piled steel platforms have the advantage of being very stable under the worst

sea conditions, but they are virtually immobile. In shallow waters the plied platforms is

probably preferred over the jacket in separate sections usually begins onshore. They are then

assembled on a flotation tanks, then up righted, and finally submerged over the chosen spot on

the seabed. The jacket is then pin-piled, the superstructure" and accommodation modules

or buildings erected, and the platform made ready for operation

Gravity Structures

This is a family of deep-water structures usually built of reinforced concrete, but may be of steel

or a combination of steel and concrete. These structures rely on gravity to keep them stable of

the seabed. Unlike piled steel platforms, they are relatively mobile and need no piling to hold

them in place. Gravity structures tolerate a wide range of seabed conditions. While they can be

used for development drilling and production, they also have the advantage of being able to

store oil in their structural cells. A typicalgravity structure consists of a cellular concrete or steel base for storage or ballast, a number vertical columns, which support a steel deck and

give access to the risers, and deck accommodation in the form of detachable

modules. Construction of the concrete type begins in a dry-deck basin where the base

caisson is partly built. The basin is then flooded and the base towed into deeper water where the

caissons are finished, the towers are formed, and the deck installed. Steel structures are

assembled in the same manner as piled steel platforms, and all types are towed to their final

destinations and settled upright on the seabed by controlled ballasting. Deck modules are then

fitted onto the deck and fitted out, after which the platform is ready for operations. There are

several configurations of gravity structure, each of which is constructed to client requirements