Construction/Installation 



The first step is preparation of the fabrication site itself, 

 including dry dock, road and rail spurs, yard, dockage, and storage 

 areas. Site preparation can take as much as three months to a year, 

 depending on the size of the facility [26]. 



When ready for fabrication, the site should be 5 to 15 feet above 

 mean high water in adjacent navigation channels. The waterfront site 

 required for a fabrication yard may involve a high probability for 

 wetland and shoreline alteration in the construction of the facility. 

 Most of the site will be cleared of vegetation and graded by large 

 earthworking machinery. Parts may require being filled and stabilized 

 with sand and gravel from adjacent waters or lands. Existing channels 

 may have to be deepened or widened to provide a turning basin and access 

 to deepwater channels for marine traffic— barges, tugs and platforms. 



Operations 



Steel platforms are made up of two sections--the deck and the 

 jacket . The jacket serves as a base to support the deck section. The 

 jacket is composed of huge steel tubular members welded together to form 

 a stable base. When completed, it is rolled on dollies or rails onto a 

 launch barge and towed to the installation site. 



The deck section includes the drilling and production facilities, 

 living quarters, helipad, and whatever else may be required, depending 

 on the complexity of the platform. The deck section and its attached 

 units are built in large construction sheds, sometimes in distant areas. 

 Wherever completed, the deck section is barged separately out to the 

 installation site. 



Gravity Platforms : The assembly of gravity platforms differs 

 markedly from that of fixed platforms. Since there is little difference 

 between steel or concrete gravity platforms, apart from materials involved, 

 the focus here is on concrete platforms. 



The base of the platform, usually composed of many cylindrical 

 prestressed concrete cells, is constructed vertically in a dry dock 

 (graving dock) immediately adjacent to deep water (150 to 300 feet). 

 When completed, in about nine months, the gravity platform is floated 

 out of dry dock; its ballast cells are filled, and the base section is 

 partially submerged to permit further vertical construction. If the 

 platform is to be used in shallow water, all that is necessary at this 

 point is to affix a deck section to the base and to add the appropriate 

 drilling, operations, storage, and living quarter modules; then the 

 platform is ready for deployment. However, since concrete platforms are 

 more often used in wery deep water, huge concrete pillars, or towers, 

 are constructed atop the partially submerged base section. The con- 



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