131 



ment, remove paraflSn, and to perform sand consolidation and various other 

 remedial work, costs of underwater comp^eltions are very high. 



In the Gulf of Mexico it costs about $550,000 to drill and complete a 12,000- 

 foot underwater exploratory well in lOO feet (30 meters) of water and to install 

 a flowline to a nearby platform." The cost for underwater wells should increase 

 in proportion to the total drilling cost of mobile rigs {Figure 1) and should 

 thus approach $990,000 in 600 feet (183 meters) of water, and $1,100,000 in 1,000 

 feet (305 meters) of water. 



This can be compared to the $4(X),000 cost of drilling and completing a plat- 

 form well in 150 feet (46 meters) of water, including a share of platform costs." 

 The cost of platform wells increases with water depth, as their share of the 

 platform cosits increase. From Figure 2, the per well share of platform cost is 

 approximately $80,000 in 100 feet (30 meters) of water, $100,000 in 150 feet of 

 water, and $600,000 in 000 feet (183 meters) of water. Thus, the cost of a plat- 

 form well can be estimated as $400,000 in 100 feet of water and $900,000 in 600 

 feet of water. 



The latter figure is roughly equivalent to the cost of an underwater completion 

 in this water depth. By projecting the curve of Figure 2 it appears that the ini- 

 tial costs of underwater development wells will be cheaper than platform wells 

 in 1,000 feet (305 meters) of water. However, operating costs of underwater 

 wells are relatively unknown at this time. 



C. PEODTTCTION FACILITIES 



After the wells are drilled, production facilities are required to permit proc- 

 essing, measuring, storing, and transporting the crude oil to a sale point. 



Offshore platform-mounted production facilities do not differ significantly from 

 those onshore. They are more expensive, however, because of the need to mini- 

 mize weight and space, and the higher costs of offshore construction and opera- 

 tion. Also, in most cases living quarters and support facilities must be provided, 

 which further increase costs. Within platform capabilities, the cost for facilities 

 should not increase significantly as water depth increases. In water depths be- 

 yond platform capability, wells will be completed under water and produced to 

 an underwater or floating production facility which can be expected to cost sig- 

 nificantly more than platform-mounted facilities. 



Although several fields have been developed with underwater completions and 

 flowlines from the individual wellheads to production facilities onshore, no 

 underwater or floating production facilities have yet been installed. However, 

 because of the demands placed on floating and underwater production equipment 

 by the environment, as well as by the varied tasks which must be performed, 

 it is clear that these facilities will be complex and costly. 



In addition, because a diver or submersible vehicle is required for surveillance 

 and maintenance, operating costs for underwater facilities will undoubtedly be 

 much greater than those of existing surface facilities. Existing submersibles are 

 mainly research vessels ; they do not presently have manipulators capable of 

 meeting the torque requirements of the offshore oil industry,^- and they are 

 costly to build and operate. 



D. PIPELINES 



Offshore pipelines in the Gulf of Mexico are between two and 4% times more 

 costly than comparable onshore pipelines." It is not possible to draw a graph of 

 cost versus water depths from existing experience since costs depend also on 

 location, size, weight and coating required, soil conditions, and wave and tide 



M "Offshore Report," Oil and Gas Journal, June 20, 1966. 

 " Ibid. 



12 Resources of the Sea, Eeport of the Secretary General. United Nations Economic and 

 Social Council (February 1968). 



13 "Offshore Pipelining," Oil and Gas Journal, December 12, 1966. 



