PETROLEUM GEOLOGY — LEVORSEN 229 



Virginia, and Indiana, together with those within the Pennsylvanian 

 sediments of the mid-continent region, are of the stratigraphic type 

 and were discovered largely by the early "wildcatter" who followed 

 whatever hunch seemed best to fit the occasion. Such drilling was 

 totally unscientific but because there were so many shallow strati- 

 graphic pools to discover, it was effective, and many fortunes were 

 built and large quantities of oil were found. 



The approach of the petroleum geologist to the problem of finding 

 traps that might contain oil has been chiefly through his ability to 

 locate favorable structural areas, either by surface or subsurface 

 geology, or by geophysical methods. However, as he is forced to 

 search deeper and deeper for his data, and as it is becoming more 

 difficult to find untested "structures," the expense keeps mounting, 

 and he is gradually turning his attention to the possibilities of finding 

 stratigraphic type pools. The ammunition he brings into use for such 

 work includes the microscope, the electric log, paleogeology, paleo- 

 geography, imagination, and speculative reasoning based on sound 

 fundamental geological concepts. The tide of exploratory thinking 

 is running strongly in tliis direction at present, and the possibilities 

 for success are almost unbelievably great. 



Probably the most important development of the past decade, 

 and an approach that is still in its infancy, is the continually widen- 

 ing use being made of well cuttings, cores, electrical logs, and all sorts 

 of detailed stratigraphic data. It calls for a technique which, in part, 

 was forced upon the petroleum geologist when drilling methods 

 changed from the use of cable tools to the use of rotary equipment. 

 At that time the driller was unable to make a satisfactory log of the 

 well he was drilling and the geologist was called on to do it for him. 

 This he did through the use of the microscope, and the resulting ad- 

 ditions to our knowledge of the stratigraphy, sedimentation, geologic 

 history, paleontology, and structure in much of the sedimentary area 

 of the United States is so vast as to make almost all previous data 

 obsolete and insignificant. 



Not only do detailed stratigraphic and sedimentation studies fur- 

 nish the background for modern subsurface work, but they are also 

 the basis for any scientific search for pools of the stratigraphic type. 

 The operator attempting to find such a pool with a minimum of drill- 

 ing is indeed sorely in need of geologic assistance. In a way it is 

 like the children's game of Hide the Button, the difference being 

 that the operator now expects the skilled sedimentationist and micro- 

 paleontologist to tell him when he is getting "hot" or when he is 

 getting "cold." 



In discussing this question of the trend of petroleum geology with 

 one of the geologists of the Gulf coast region, I could not help but 

 agree with him when he stated that, in his opinion, the trend could 



