In addition to the deep penetration seismic survey activity described 

 above, other types of surveys are performed, such as shallow penetration 

 high resolution acoustic (sonar) studies to locate ocean floor geologic 

 hazards such as faults and mudslides. Results of these surveys are used 

 to aid in the selection of specific exploratory drilling and production 

 drilling sites. 



Another type of survey involves the use of a magnetic sensor or 

 magnetometer to locate anomalies. The magnetometer is towed behind the 

 survey ship, similar to a seismic survey. The data is interpreted to 

 detect small warps or anomalies in the earth's magnetic field produced 

 by the different types of rocks. These anomalies indicate the structure 

 of subsurface rocks and petroleum-bearing strata. 



Survey vessels often use gravity meters to measure slight changes 

 in the force of gravity attributable to different rocks of varying 

 densities over which the vessel passes. 



The geophysical survey data collected by one or more techniques 

 described above may be supplemented by geologic studies of rock outcrops 

 on or near the sea bottom. The goals of these studies include age 

 determination, stratigraphic correlation assessment of the lithologic 

 character, and evaluation of mechanical properties (such as load strength 

 and compressibility), necessary for design of platforms and pipelines in 

 specific locations. 



A process that may conclude this phase is drilling a Continental 

 Offshore Stratigraphic Test (COST) well. Core samples taken during 

 drilling are used to confirm conclusions about the rock layers and 

 structural composition of the rock. These tests, drilled from a 

 mobile rig, may penetrate up to 16,000 feet. According to USGS regu- 

 lations, stratigraphic test wells must be drilled off of any presumed 

 geologic structure and no direct testing for oil and gas is permitted. 

 The data obtained from analyzing the test must be released within 60 

 days after the initial lease sale in the area. Various well logging 

 tests and an evaluation of drill cores and cuttings can be used to 

 analyze the geologic sections that indicate the presence of source and 

 reservoir rocks and other factors which are indicators of possible 

 petroleum accumulations in the adjacent structures. 



Two deep stratigraphic tests financed by a consortium of more than 

 20 companies were completed in the Baltimore Canyon trough in the spring 

 of 1976 and in the Georges Bank area during the summer of 1976. 



Site Requirements 



With the exception of COST holes, geophysical survey has no 

 significant onshore siting requirements. The survey vessel, requiring a 

 berthing space, is similar in size and needs to a commercial fishing 



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