CHAPTER 14 

 SUBSURFACE METHODS AS APPLIED IN GEOPHYSICS 



HARRISON E. STOMMEL 



Since the introduction of geophysical methods of prospecting in this 

 country in the early 1920's, refinements in instrumentation, in field pro- 

 cedure, and in interpretation have made geophysics the foremost explora- 

 tion technique available to the oil industry. In recognition of its successes 

 the larger oil companies have created geophysical departments on a par 

 with their geological departments. The location of new reserves has be- 

 come of such major importance that most oil companies now rank the 

 exploration division, usually headed by a vice president, with the pro- 

 ducing, pipe-line, refining, and marketing divisions. Coffin ^ states : 



The exploration budgets of at least three companies whose geological 

 and geophysical expense exceeds five million dollars yearly carry items for 

 geophysical expense in excess of total geological expense in ratios ranging 

 between 5 to 1 and 10 to 1. 



Few petroliferous provinces exist where surface mapping alone gives 

 evidence of subsurface structure. In this country, for example, the entire 

 Gulf Coastal Plain, the Midcontinent, the Great Plains, Western Canada, 

 and a part of California are blanketed by a thick series of younger sedi- 

 ments which are often unconformably related to the deeper potential- 

 reservoir rocks. In such areas the combined efforts of subsurface geologist, 

 the paleontologist, and the geophysicist are required to locate new ac- 

 cumulations. Finding another East Texas, Slaughter, or Yates field is 

 considered very unlikely by the geologist or geophysicist, his efi^orts being 

 directed to the location of smaller and deeper structures that were over- 

 looked in the past or to prospecting in new, less favorable areas. 



In the mining industry the future of geophysics looks exceedingly 

 bright. Within the past several years a number of the country's largest 

 metal producers have added geophysicists to their exploration staffs and 

 are at present engaged in geophysical field work and research. Although 

 geophysics was first applied to the location of mineral deposits in the 

 1600's, refinements in technique have not kept pace with the needs of the 

 mining industry. This is not solely the responsibility of the mining geo- 

 physicist. He has been hampered by a lack of research funds, by the most 

 complex geologic situations possible, and by the small size of the target. 



It is rumored that new electrical techniques are being developed by 

 the mining industry which show promise of much greater resolving power 

 than has heretofore been achieved. Mining geologists today feel the need 

 for additional tools to aid them in mineral exploration, because attention is 



^ Coffin, R. C, Recent Trends in Geological-Geophysical Exploration: Am. Assoc. Petroleum Geolo- 

 gists Bull., vol. 30, no. 12, p. 2014, Dec. 1946. 



