A Potential Sources of Disturbance subsection provides information 

 on sources of ecological disturbance that affects fish and wildlife 

 and their habitats. Individual subproject discussions acquaint the 

 reader with project-specific features of the standard subprojects 

 discussed in Part 4. The designation "SP-" plus a numeral in 

 parentheses following the subproject title refers to the standard 

 subprojects list given in Table 2. 



3.1 OFFSHORE RECOVERY AND TRANSMISSION SYSTEMS 



3.1.1 Profile 



The process of recovering oil and gas from offshore fields can be 

 broken into a number of fairly well-defined steps. Although these occur 

 in sequence for any given tract over an entire field, several steps may 

 proceed concurrently as new lease sales occur or sponsors carry out their 

 exploration and development plans at different paces. This sec tion embraces 

 the normal range of offshore development projects, i.e., surveying, drilling, 

 and installation and operation of platforms. Pipelines, offshore moorings, 

 and operation of tankers are addressed in Section 3.2. 



Once a prospective field is identified and a lease sale announced, 

 the recovery process begins with a massive data-gathering effort. Con- 

 tractors gather stratigraphic and seismic data for each of the oil com- 

 panies for interpretation by geophysicists and geologists. Based upon the 

 interpreted data, oil companies bid for leases on available tracts. Success- 

 ful bidders conduct exploratory drilling and, where successful, platforms 

 are placed for development drilling and production. The products are de- 

 livered to shore through a pipeline laid on the seafloor or via tanker. 



3.1.2 Site and Route Requirements 



Site selection for an offshore platform is based upon subsea surface 

 characteristics, oil or gas reservoir characteristics, ownership of adja- 

 cent tracts, and US6S lease stipulations. The most important factor is 

 subsurface geology. Bottom conditions, including surface sediments and 

 relief, limit feasible locations. From a construction standpoint, steep 

 slopes and soft sediments are undesirable bottom conditions. 



3.1.3 Potential Sources of Disturbance 



The major ecological disturbances caused by offshore development are: 

 (1) water pollution caused by discharges during drilling, (2) water pollution 

 caused by discharges during pumping and preliminary processing of the oil 

 stream on the platform, (3) pollution caused by oil spills from well blowouts, 

 and (4) disruption of benthic organisms. Accidental releases of gas are con- 

 sidered to be ecologically inconsequential. Exploratory activities (seismic 



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