Introduction
There are more than 6,500 offshore oil and gas installations around the world, in some 53 countries.
The main areas are:
- US Gulf of Mexico: 4,000
- Asia: 950
- Middle East: 700
- Europe, North Sea and North East Atlantic: 490
- West Africa coast: 380
- South America: 340
These installations are built for varied applications:
- Drilling.
- Preparing water or gas for injection into the reservoir.
- Processing oil and gas.
- Cleaning the produced water for disposal into the sea.
- Accommodation facilities.
Many different types of platforms exist, but we paid particular attention to fixed structures.
A fixed platform may be described as consisting of two main components, the substructure and the superstructure.
Superstructure: also referred as the 'topsides' supported on a deck, which is fixed (mounted) on the jacket structure. These consist of a series of modules which house drilling equipment, production equipment including gas turbine, generating sets, pumps, compressors, a gas flare stack, revolving cranes, survival craft, helicopter pad and living quarters with hotel and catering facilities. It can weigh up to 40,000 tonnes.
Substructure: is either a steel tubular jacket or a prestressed concrete structure.
Most fixed offshore oil and gas production platforms have a steel jacket although a small
number of platforms have a concrete foundation. Each platform is uniquely designed for the particular reservoir condition, location, water depth, soil characteristics, wind, wave and marine current conditions. Fixed steel and concrete
platforms can be built in water depth from a few meter to more than 300 m.
 Steel Jacket structure
|  Concrete gravity base
|
In the North Sea for example, large platforms have to cope with some of the most severe environmental
conditions in the world. They must be able to withstand a hundred-year return period wave
with a height of up to 31 m and a wave period of between 15 and 20 seconds. The storm duration
is commonly assumed to be 6 hours. They must also be able to withstand wind speeds of 220 km/h. The same parameters are taken into account in the design of offshore platform in other world wide locations.
North Sea has the greatest concentration of large steel jacket structures in the world (25%-30% of the world total).
|
| North Sea
| UK
| Water Depth
|
| Steel jacket structure
| 300
|
| < 75 m
|
| Steel jacket structure
| 100
|
| >75 m
|
| Steel jacket structure
|
| 216
|
|
| Concrete gravity base
| 25
| 11
|
|