lent tool in localizing many of the earlier leads, and routine core drilling of 

 large areas developed many new structural prospects. Amprex's geologists fol- 

 lowed a program of first core drilling the leads and then processing large acreage 

 blocks along the most attractive trends of the basin. 



As the detailed exploration progressed, outlines of some prospects changed, 

 new prospects were discovered and leased, some leads were eliminated, and 

 ideas changed as additional data filled in the information obtained by the recon- 

 naissance surveys. Significant were the changes and revisions in geological 

 thinking as more became known of the surface and subsurface of the area. Many 

 of the old hypotheses were strengthened, some were revised, and new ones were 

 developed. The positions of regional structural and stratigraphic trends within 

 the basin were modified. Their generalized position as now visualized by Am- 

 prex is shown on Figure 41-16; form contours show the structural anomalies. 



The landmen continually expanded and changed their buying outlines as 

 the areas were revised. Titlemen and lawyers began examining titles of owner- 

 ship on tracts of land covering the most attractive prospects, anticipating the 

 early wildcatting of these areas. Civil engineers were assigned the task of de- 

 termining physical, political, and legal boundaries in these high-priority areas. 



Wildcat Drilling Operations 



Approximately 18 months after Amprex had begun its detailed exploration 

 program, it was ready to drill some of the more attractive prospects. Almost 

 three years had elapsed since the first company geologist had questioned the 

 possibilities of the area. Almost six million dollars had been expended in in- 

 vestigating the area. The next operation to many was the most exciting phase 

 of exploration — wildcatting. 



Of the many prospects that Amprex had developed in exploring the basin, 

 perhaps the most interesting and the most prospective was the one originally 

 located by the drilling of the Amprex No. 1-C stratigraphic test. It will be 

 recalled that this test found a possible reef or near-reef facies in a Devonian 

 dolomite section which carried oil staining in the cores and cuttings. When 

 drill-stem tested, this section actually flowed salt water with a rainbow of oil. 

 When detailed exploration was begun, this was one of the first areas to be 

 worked by the seismograph and also one of the first areas to be core drilled. 

 Both seismic data and core-drill structure maps showed a well-defined anticline. 

 The core-drill information (fig. 41-17) contoured on shallow Permian beds 

 indicated a low-relief anticline approximately fourteen miles long having a 

 north-south trend, while the seismic data (fig. 41-18) contoured on a horizon 

 that was estimated to be the approximate top of the Devonian defined a major 

 anticline having approximately the same shape and size as that of the shallow 

 structure. Steep and erratic seismic dips occurring along the flanks of the 

 structure, in what was correlated to be the Silurian-Devonian section, strongly 



846 



