work and exploratory drilling) involve such minor disturbance to marine 

 life, and to human uses of the ocean, that they are not discussed here. A 

 past practice in seismic activities involved the use of dynamite and other 

 explosives to generate the shock waves for geologic analysis. This prac- 

 tice has been abandoned by most progressive companies. If the practice is 

 proposed, literature is available on the impacts of such activities. 



Subproject: PCS Platforms and Offshore Structures (SP-18) 



Disturbing Activities: Installation, operation 



Although offshore platforms can have adverse physical effects 

 on the seafloor life below, greater damage may be wrought by inade- 

 quate operational safeguards. Sizable oil spills may occur during 

 drilling or production if formation pressure exceeds that which 

 is anticipated. 



Other possible disturbances that may occur include chronic discharges of 

 oily formation water (brines) from platforms during production, disposal of 

 drill cuttings and drilling mud during exploration and development (Table 7), 

 and disposal of trash, garbage, and sewage. Properly controlled, the com- 

 bined effect of disposing of these wastes is unlikely to be significant, 

 unless the platform is located in an ecologically vital area. Improperly 

 controlled, the effects can be significant; for example, the release of oil 

 along with the discharge of "formation water" is in violation of EPA restric- 

 tions (maximum, 50 ppm oil) [2]. 



3.2 OFFSHORE OIL AND GAS TRANSMISSION SYSTEMS 



3.2.1 Profile 



This section discusses systems used for delivering offshore oil and 

 gas to shore and for transferring and reshipping crude and processed 

 hydrocarbons over or under the sea. The principal components of these 

 delivery or transmission systems in current use are: (1) tankers or barges 

 that may receive hydrocarbons directly from offshore wells, or, more likely, 

 from onshore reshipment terminals; (2) offshore mooring and transfer sta- 

 tions for tanker loading from wells or for transfer of hydrocarbons at sea; 

 and (3) pipelines used for direct transmission of hydrocarbons from off- 

 shore wells to onshore facilities. 



Tanker operations can release oil in a number of other ways. Great 

 tanker catastrophes, such as the spillage of 700,000 barrels of oil from 

 the 118,000-ton tanker Torrey Canyon in 1967, are widely known. But the 

 major source of oil pollution from tankers is intentional discharge, i.e., 

 the pumping of oily ballast water and tank washings into the oceans. 

 Modern oil tankers may range from 19, 000-ton -ships, used to transport oil 

 short distances, to 500,000-ton supertankers. A 100,000-ton tanker is 



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