Tension Leg Platforms (TLP)
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General
Description
A Tension Leg Platform(TLP) is suited for oil and gas production from 2000 ft to 5000 ft water depths. Currently there are about 24 TLP's installed. The structure is held in location using thick steel pipes called Tendons (generally 24-42 inch diameter, 1 inch thick). The tendons give the structure a very high stiffness, such that even in extreme waves the TLP does not heave significantly. There is however, a huge horizontal offsets since there are generally no, or very little, horizontal stiffness associated with the structure.
The tendons are designed with very high stiffnesses such that the natural heave period of the structure is close to 3-5 second range. This is away from the predominant wave periods, and avoids resonance.
Due to limited heave motions, the stroke of the risers is small, and hence a Top Tensioned Riser system is generally used. This gives a direct access to the well. Also, if there is a workover rig present on the TLP, it generally, eliminates the requirement of a drilling vessel in case of small workovers or well interventions.
Some of the TLP's installed today are
- Magnolia
- Kizomba A
- Kizomba B
- Marco Polo
- Shenzi
- Neptune
Advantages
- It can be fabricated and commissioned at the quay side with only offshore installation being tendons.
Disadvantages
- Cost of the tendons is comparable to the main hull cost.
- Installation is a risky operation.
Other
The selection of a TLP over other existing solutions depends completely site specefic and can not be generalized.
