Table 5. Factors affecting the number and locations of onshore support facil' 

 ities (New England River Basins Commission 1976a; 1976b). 



Location of oil and gas field 



Size of oil and gas field 



Topography of oil and gas field 



Depth of water 



Whether both oil and gas are found 



Availability of coastal frontage (land) 



Availability of additional (back-up) land 



Proximity of existing refineries and processing plants 



Proximity to diverse urban areas and markets 



Public services and facilities (schools, hospitals) 



Labor markets (areas without strong labor unions are preferred) 



Public opinion 



Availability of entertainment 



Proximity to airport or landing strip 



Service bases require at least two berths, each about 122 m (400 ft) long 

 per rig. Fewer vessels and helicopters may be required if several rigs are 

 serviced from the same service base. Depending on the distance to the rig and 

 the nature of offshore DCS operations, at least two vessel trips and one heli- 

 copter trip per rig are required daily. The typical types and quantities of 

 materials transported offshore to a drilling rig in one year are shown in 

 Table 6. 



Temporary service bases are established as soon as exploration and early 

 development begin. Temporary bases may be expanded into permanent service 

 bases, but only if a significant discovery of oil or gas has been made. 

 Pipeline installation service bases locate during the latter part of the 

 development phase; preferred locations are pipeline landfall sites and pipe 

 casting yards. Preferred locations for platform installation service bases 

 are sites within close proximity to where platform installation will occur. 



Transportation Facilities 



Pipelines are the preferred method of transporting oil from offshore to 

 onshore locations although tankers sometimes are used. Gas is always trans- 

 ported by pipeline. The locations of pipelines usually depend upon decisions 

 based on distance from shore (the shorter the better), and environmental con- 

 siderations, e.g., ocean bottoms, and landfall beaches. The location, costs 

 and suitability of pipeline easements also are important considerations. Usu- 

 ally the production threshold that must be met to justify the construction of 

 a pipeline is 70,000 bbl per day for oil and 500 million ft^ per day for gas. 



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