affect marine ecosystems--location and operation of platforms--are 

 made almost exclusively by the company and approved by USGS. Major 

 disturbances that arise from inappropriate placement and inadequate 

 operational safeguards are benthic disruption and spills caused by 

 accidents related to the well casings and blowout prevention valves. 

 Other lesser impacts are caused by pollution from drill cuttings and 

 mud and leakage from abandoned wells. On the other hand, platforms 

 often attract an abundance of fish and become popular fishing spots. 



Placement of Structures : While actual installation of a platform 

 is a minor concern, its location may be the key determinant of its per- 

 manent ecological effects or benefits. If properly placed, the platform 

 will avoid any vital areas, such as shellfish beds, spawning grounds, 

 rich feeding areas of commercial fishes, and critical flyways of migra- 

 tory birds. Structures should also avoid productive fishing grounds 

 and navigational routes. Any vital areas outside the lease area but 

 wihtin the trajectory of a significant spill from the platform should 

 be known so that sites in areas of special biological significance 

 can be avoided. 



There are three requirements for information that precede the 

 approval of a platform site. First, all ecologically vital and other 

 critical areas (fishing, anchoring, ship lanes) in the lease area must 

 be identified and described. Second, the probable trajectories of oil 

 spilled at proposed platform sites should be appropriately computed. 

 Third, all ecologically vital and other critical areas within range of 

 a significant spill must be identified and described. 



Dril ling : The complex ecological requirements for OCS drilling 

 operations are the subject of much interaction between the FWS and other 

 agencies and are so site-specific that generalization is quite difficult. 

 The subject is discussed briefly below. 



The major concern is well blowouts (from subsurface pressures) 

 which can cause substantial releases of hydrocarbons into the water. It 

 has been reported that on the average one blowout occurs for every 2,860 

 offshore wells drilled [2]. The famous Santa Barbara spill occurred 

 from subsurface escape of oil through a weak geological structure which 

 fissured at the ocean floor. Much more common are blowouts that come 

 up through the well casing and are not stopped by a blowou' preventer. 

 In drilling, this may start because the drilling mud is not heavy 

 enough to hold down the pressure, but ultimately the cause is a defec- 

 tive, inactive, or missing blowout preventer. Effective blowout pre- 

 venters, as well as "downhole control devices", also function during 

 topside accidents or emergencies to prevent large amounts of oil from 

 escaping. It has been noted that "when hurricanes have passed through 

 offshore oil and gas fields, entire platforms have been swept away with 

 only minimal spillage" [107]. Constant surveillance may be required to 

 assure that the well operators keep the preventers in place and in good 



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