Offshore Rigs

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1- Barge rig

These are small, flat-bottomed vessels that can only be used in very shallow

waters such as deltas, swamps, lagoons and shallow lakes.

2-Platform rig

Platforms are permanently fixed structures installed where mobility is not

required. This is typically when multiple wells are going to be drilled to

develop and produce a field.

Platforms can be of:

1- Steel jacket 

2- Caisson type

3- Concrete gravity

Compliant platforms rigs can be:

4- Guyed-Tower    

5- Tension-Leg


3- SEMI- SUBMERSIBLES

“Semi-subs” are floating rigs that are suitable for drilling in deeper waters than jack-ups. The deck is supported by a number of legs or columns. Sub sea, these columns are supported by pontoons which can be solitary or connected. Both pontoons and columns are utilized to ballast and stabilize the rig.

Advantages

1- Can work in water up to 2000 ft.

2- Has a god safety records.

3- Provides a relatively stable platform.

4- Can be self propelled

Disadvantages

1- Need marine risers and Sub Sea stack.

2- Has limited cargo capacity.

3- Requires support vessels.

4- Submersible

Early design for deeper water > 30 feet, Replaced by jackups, Submersible can be of

5- Jack up

These are mobile vessel suitable for drilling in shallow seawater depths. They consist of a fixed hull or platform, which is supported on by a number of legs, typically 3, that stand on the seafloor.

Advantages

1-Those rigs drill in water depths up to 400 ft (120m)

2- Provides a fixed platform at low initial cost

3- Does not need a marine riser or sub sea stack.

4- Can operate in soft bottom deltas

5- Can withstand storms.

Disadvantages

1- Poor safety records

2- difficult to tow

3- Have moving part in jacking mechanism

4- hazardous for going on and off locations

6- Drill ship

Advantages

1- Can work in ultra deep water; more than 2000 ft.

2- Self propelled.

3- High carrying capacity

Disadvantages

1- Need marine risers and Sub Sea stack.

2- Not as stable as jackups and semi sub.

 

-Motion Compensating System

This system is used entirely on offshore floating rigs, semi-submersibles

and drill ships.

Marine Riser-

Functions

– A large diameter pipe that connects the sub sea BOP’s to a floater.

– It provides a path for the drilling fluid, from the borehole to the rig

– To guide the drill string and other tools to the wellhead on the sea floor