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THE FUTURE OF 

 SUBSURFACE 

 PETROLEUM 

 EXPLORATION 



A. I. Levorsen 



The usefulness of subsurface geological methods in petroleum exploration 

 and production problems has increased steadily since the beginning of the petro- 

 leum industry. As more subsurface understanding is called for, more and more 

 geologists become specialized in this type of work, until in many areas practically 

 all of the exploration geology is based on subsurface interpretations. 



PETROLEUM Petroleum exploration in most regions has 



EXPLORATION followed a logical sequence in that it has pro- 



ceeded from the known and obvious to the less 

 known and less obvious, from surface geology toward subsurface geology. Once 

 the anticlinal theory of oil and gas accumulation was accepted, it was only natural 

 that all anticlines that could be observed at the surface should be mapped and 

 tested by the drill. This was followed by structure mapping at shallow depths by 

 core drilling, by subsurface mapping within the reach of the drill, and at all 

 depths by geophysical methods. The search for structural traps may be called 

 Phase I in the orderly sequence of exploration. 



As favorable closed structures in a region become increasingly difficult to 

 locate by any available means, attention is directed to traps in which local struc- 

 ture is but a part of the reason for a trap, the other part being some stratigraphic 



