result in impacts beyond the sum of the simple effects. The results of combi- 

 nations of activities may be complicated, unpredictable, and require a broader 

 perspective than most people are accustomed to using. 



The decision process for planning wells considers the petroleum pricing 

 structure; tax laws; economic forecasts; government regulations; international 

 trade; and financial climate. As a result, oil and gas fields are not devel- 

 oped according to a single plan over a short period of time. They develop 

 according to incremental changes in knowledge and conditions. Thus, the 

 impacts from the second level of oil and gas activities are not predictable 

 and are presently controlled only through management applied at the individual 

 activity level. 



Purpose 



The purpose of this chapter is to describe in detail the activities that 

 are associated with oil and gas exploration and production. Particular atten- 

 tion will be given to those activities that affect fish and wildlife. 



Overview of Phases of Oil and Gas 

 Activities Found On and Off Refuges 



For the purpose of this study, oil and gas activities take place in three 

 general areas: dry land, marshland, or shallow coastal waters near land. 

 While each of these generalized areas may correspond to more than one ecosystem 

 - for example, marshes may include fresh, intermediate, brackish, and saline 

 types - the techniques used by the oil industry are mainly dependent upon the 

 characteristics of the three distinct environments. 



Preexploration reconnaissance. Oil and gas exploration begins with a 

 broad reconnaisance of the area. Many geologic features indicate the presence 

 of petroleum-bearing formations, broad reconnaissance methods have wery 

 little effect on wildlife in the area. 



Seismic surveys. After a prospective area is chosen, site-specific 

 geophysical surveys are made. Generally these require direct access to the 

 land or water surface under which the minerals may lie, and they may necessi- 

 tate authorization, permission, permits, and payments to the mineral and 

 surface owners. Many of the geophysical surveys utilize seismic methods, 

 whereby shock waves transmitted to the deeper strata are reflected back to 

 receiving units in the immediate area. Since strata may have characteristic 

 shapes, refractions, and differences in reflectivity, it is possible to con- 

 struct maps of the different formations. These maps are then examined carefully 

 for structural features that are characteristic of oil and gas deposits. 

 Other geophysical methods rely on measuring changes in strength or direction 

 of fields. 



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