Description 



Production platforms may be fixed-pile platforms or gravity platforms. 

 Gravity platforms may be constructed with cement or steel as the major 

 component. All platforms consist of two parts: the deck and the jacket. 

 The jacket, which serves as a base supporting the deck section, is the 

 large skeletal framework often visualized when offshore oilfield develop- 

 ment is discussed. 



The fixed-pile platform, commonly used in the United States, is a 

 steel framework. A fixed-pile platform is shown in Figure 15. Gravity 

 platforms, using concrete in the North Sea and steel off West Africa, 

 are rather recent innovations. The comparative advantages and liabilities 

 for selecting a gravity or a fixed-pile platform are discussed later. 

 At the present time industry anticipates all platforms used in United 

 States OCS frontier development will be the fixed-pile platform type. 



The deck assembly includes modular units that may be interchanged 

 for each of the three operations conducted on a production platform: 

 production drilling, routine maintenance, and workover. Production 

 wells are drilled with a derrick. Figure 16 illustrates a production 

 platform drilling several wells. Pipe, drilling muds, and other necessary 

 equipment are periodically shipped to the platform and stored on board. 

 After wells are drilled, the drilling equipment is removed, so that only 

 crew quarters, monitoring, and safety equipment remain. As many as 

 sixty wells may be drilled directionally from a single platform. 



Site Requirements 



A production platform is situated within a leased tract, a square 

 usually encompassing approximately 9 square miles. A platform may 

 generally be situated at any location in the tract. This location is 

 restricted when the adjacent tract is owned by another company. Companies 

 that will be in different tracts but will share a common reservoir (oil 

 bearing geological structure) will try to establish a joint venture. 

 The U.S. Geological Survey also desires and may require joint ventures 

 ("unitization") to achieve the Maximum Effecient Rate (MER) of the 

 reservoir. Several factors influence selection of a specific site 

 including subsea surface characteristics, reservoir characteristics, 

 ownership of adjacent tracts, and lease stipulations controlling 

 activities within. 



The greatest single factor in selecting a location for a platform 

 is a subsurface geology. Bottom conditions, including surface sediments 

 and relief, limit feasible locations. Steep slopes and soft sediments 

 are undesirable bottom conditions. If oil is found under these surface 

 conditions, directional drilling, which has a horizontal range of 

 approximately one mile, is one method for overcoming the problem. 



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