estimated cost of $50,000 to operate a seismic crew for a month, the annual 

 expense of one seismic crew would absorb $600,000 of the budget. It was 

 important, therefore, that the seismic effort be concentrated in the more at- 

 tractive areas. 



In order to determine the more attractive areas, four stratigraphic tests 

 were drilled, each being located in a different part of the basin (fig. 41-5). The 

 objective of these tests was not to explore a potential structure or stratigraphic 

 trap for oil and/or gas, but rather to evaluate the sedimentary section. Of pri- 

 mary interest to the geologists at this stage of exploration was the thickness 

 and character of the sedimentary section in the various parts of the basin. 

 Each test provided basic information vital to both geological and geophysical 

 exploration. From a careful study of the cores and cuttings recovered by each 

 test, the paleontologist, the petrologist, and the petrographer determined the age, 

 the lithology, and the environmental and depositonal history of the rocks en- 

 countered in the hole. By correlating this information with similar information 

 obtained from studies of the outcropping rocks around the margins of the 

 basin, the geologists were able to refine their subsurface thickness, structure, 

 and facies maps. The geophysicist ran velocity logs and made density measure- 

 ments to assist the seismologist and the gravity computers in interpretations of 

 their data. Where basement was encountered, cores were taken and analyzed 

 by the geophysicist for susceptibility and other magnetic properties. Various 

 types of electrical surveys and gamma-ray and neutron logs aided in the inter- 

 pretation of lithology, porosity, and formation fluids. A formation test was 

 made opposite each permeable section; and subsurface fluids, where recovered, 

 were forwarded to the Geochemical Section for analyses. Subsurface pressure 

 measurements made during each formation test were studied to establish the 

 regional pressure gradients and patterns for the potential reservoirs of the basin. 

 In addition, temperature and continuous dip-meter surveys were made of each 

 of the holes. Cuttings and cores from each stratigraphic test were examined 

 closely for any possible oil staining, for one of the most encouraging facts that 

 a geologist can establish in any area is the presence of oil and gas shows. From 

 the geochemical analyses of the subsurface fluids, crude isosalinity maps were 

 constructed. The subsurface waters were analyzed for the presence or trace of 

 either crude oil or natural gas. The information obtained from these four 

 stratigraphic tests was invaluable and, as a result, Amprex concentrated its 

 early exploration and lease acquisitions in those parts of the basin offering the 

 best potentialities. 



For competitive reasons, each of these tests was drilled as a tight hole. No 

 information was released to either competitors or the public, and the distribution 

 of the basic data derived from these tests was restricted to key personnel of the 

 Exploration Department. 



824 



