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发表于 2008-5-16 09:14
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来自： 新加坡
Concrete gravity platforms
A concrete gravity platform is one that is placed on the seabed and by its own weight is capable of withstanding the environmental forces it may be exposed to during its lifetime. Most of the platforms are additionally stabilised by skirts that penetrate into the seabed.
These platforms are huge in size and weight. Some of them are among the most impressive structures ever built. e weights of the concrete substructures range from 3,000 tonnes to 1,200,000 tonnes, and support topsides weighing from between 5,000 to 52,000 tonnes. Some of the concrete substructures have oil storage ranging from 400,000 to 2,000,000 barrels (approximately 50,000 to 270,000 tonnes).
Main purpose of most concrete gravity platforms was to provide storage facilities for oil at the offshore location at a time when no, or few export pipelines were available for transport of oil from the oil fields to shore. e aim was to provide sufficient storage capacity in the platform base storage cells to enable continued production from the field. e stored oil would then typically be pumped from the platform storage cells via an offloading system to shuttle tankers. Concrete structures were also designed to provide sufficient support for topsides loads of more than 50,000 tonnes
The requirement for new fixed concrete structures with offshore storage capabilities has gradually decreased with the development of offshore pipeline infrastructure and the introduction of new technology including sub sea engineering, flexible risers and based on Floating Production Storage and Offloading installations (FPSOs).
One advantage of the concrete gravity based structures compared with conventional piled steel jacket structures, was that they could be floated/towed out to the installation site and installed with the topsides already in place. e installation could thus to a great extent be completed onshore/inshore before tow-out to the field, thereby minimising offshore hook-up and commissioning work.
Since the 1970s, several concrete platform designs have been developed. Most of the designs have in common a base caisson (normally for storage of oil) and shafts penetrating the water surface to give support for the topside structures. e shafts normally contain utility systems for offloading, draw down and ballast operations, or they serve as drilling shafts.
The most common concrete designs are:
• Condeep (with one, two, three or four columns)
• ANDOC (with four columns)
• Sea Tank (with two or four columns)
• C G Doris
• Ove Arup
The first concrete gravity platform to be installed in the North Sea was a C G Doris platform, the Ekofisk Tank, in Norwegian waters in June 1973. During summer 1975, three other concrete platforms were installed, two Condeeps and another C G Doris platform; all placed in the UK sector of the North Sea. |
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