Type of Offshore Structures

Right now, I want to share what I have learned in school about offshore structures. There are different type of offshore structure based on geometry and behavior.

1. Fixed  Platform

The fixed platform has low natural period and low deflection against environmental loads.  The two types of fixed platform:

 a.       Steel Template Platform

This is the main type platform used in Indonesia. This type is economically feasible for installation on water depth up to 500 m. This template type will be fixed to seabed by tubular piles driven through jacket leg.

b.      Concrete Gravity Structures

This type used in the harsh environments where there is not feasible to perform pile installation. The seabed has rocky condition or sandy formation. The concrete gravity structure has been constructed in water depth up to 350 m. This concrete gravity structure rest on ocean floor by virtue of their weight. Several design have cellular concrete foundation or caisson to support deck structures.

     2. Complaint Structures

         a. Tension Leg Platform

       

       TLP is vertically moored floating structure normally used for the offshore production oil and gas, practically suited for water depth around 1000 m to 1200 m. The platform is permanently moored by means of tethers  or tendons group at each TLP has been designed for site specific application, it has integral drilling/work over facilities, no oil storage, and single drilling center. TLP in Indonesia is in West Seno, Makasar Strait.

         

         b.Articulated Tower

         Articulated tower is an extension of TLP. The tension cables are replaced by one single buoyant shell with sufficient buoyancy and required restoring moment against lateral loads. The parts of articulated tower from above to the lowest: deck, upper shaft, buoyancy chamber, lower shaft, ballast chamber, connector, the universal joint which connects the shell with the foundation system, and base.  The articulated tower primary ability is to displace from its  initial position when subjected to environmental loads and reduce the maximum internal response on structural elements.

http://www.offshore-technology.com/projects/west_seno/

     3.  Floating Structures

  

Floating Production System consists of semi-submersible unit which is equipped with drilling, production, storage, or offloading equipment. It is anchored in place with wire rope and chain, or can be dynamically position using rotating thrusters. The FPS (Floating Production System or FPSO( Floating Production Storage Offloading) can be used in range of water depth from 600 m to 2500 m. The FPSO that already operate in Indonesia is FPSO Belanak.