to basin deposits. They set out to locate flexures, fault zones, or other types of 

 aligned structures which might help them to localize the hinge belt within the 

 structural framework of the basin. 



Geological and Geophysical Operations 



Utilizing the subsurface information obtained from the four stratigraphic 

 tests, Amprex's geologists revised their regional structure, thickness, and facies 

 maps. While the tests were being drilled, the company revised its seismic pro- 

 gram in order to concentrate the initial seismic energy in the most attractive 

 areas of the basin. Two seismic crews were contracted from Trans-World 

 Geophysical Company, one of the contract companies which had shown pro- 

 gressive action not only in instrumentation and seismic techniques, but also in 

 interpretation of geophysical data. Company geophysicists were assigned to 

 work with the contract group in both the field work and the interpretations. Two 

 gravity-meter crews were contracted from Geo-Service Exploration Company 

 to make a gravity survey, and at the same time, a contract was made with Air- 

 borne Magnetics, Incorporated, to make an airborne magnetic survey of the 

 basin. 



The initial seismic work was of a regional nature and was designed to 

 distinguish the major structural features of the valley. A grid of west-east and 

 north-south seismic profiles (fig. 41-5) was programmed with several of the 

 lines being located to pass through the proposed locations of the stratigraphic 

 tests. "Shooting" along the dip profiles, lines A-A', B-B', C-C, and D-D' were 

 completed prior to the three north-south or strike profiles. The four stratigraphic 

 test wells had been drilled before seismic work was completed along the north- 

 south lines; and, as mentioned previously, seismic velocities had been measured 

 in each of the holes. Stratigraphic information and velocity measurements ob- 

 tained from the test wells provided the seismologist with accurate information 

 with which to interpret seismic records and to correlate properly reflections 

 along the profile lines. 



While the geophysical work progressed, Amprex's geological staff, in 

 addition to supervising the drilling of the stratigraphic tests, attempted to 

 improve their understanding of surface and subsurface geological relationships. 

 A reconnaissance geological map of the basin was prepared by four teams of 

 surface geologists who had been assigned different areas of the basin to map. 

 Research specialists, including macro- and micro-paleontologists, petrographers, 

 structural geologists, and photogeologists, advised the surface men on special 

 problems and helped to unravel some of the complex features encountered in 

 mapping. They also made porosity and permeability measurements and ex- 

 amined various facies for evidences as to their environments of deposition. From 

 the various types of information obtained, it was possible for the exploration 



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