4 Subsurface Geologic Methods 



of reservoir rocks and their fluids, time and place of progressive structural 

 developments as well as the present normal strike and rate of dip for each 

 "layer of geology." . . . Not only is there need of a greater store of geological 

 information but also of well established criteria by which such data may be 

 used more effectively. Much progress has been made toward the development 

 and use of methods for recognition of favorable regions, localities, and well 

 locations, but more definite analysis is no doubt possible as well as highly 

 desirable.2 



The subsurface geologist is scheduled to play a major role in ful- 

 filling these requirements. 



In the early history of drilling, little attention was given to the de- 

 tailed characteristics of subsurface conditions; as a result, many geologic 

 data were lost or so imperfectly recorded that reliable interpretations are 

 now difficult to make. Present-day programs require systematic and accur- 

 ate subsurface recordings. These requirements have vastly improved such 

 problems as (1) exact structure contouring; (2) accurate definition of 

 fault patterns and their relationship to oil-producing intervals; (3) the 

 location and evaluation of unconformities; (4) facies changes and thick- 

 ness trends; (5) the interpretation of geophysical data; (6) the origin, 

 migration, and accumulation of hydrocarbons; (7) building, bridge, and 

 dam foundations and tunneling; (8) locating and outlining ore bodies; 

 (9) improvement of surface drainage systems; (10) evaluation of ground- 

 water patterns; and (11) interpretation of soil data. 



The decipherment of certain of these problems offers little difficulty 

 and thus requires only a few techniques. Other subsurface conditions 

 may be of such complexity that voluminous data are needed before logical 

 and satisfactory answers become evident. 



Noble ^ recently made the following statement: 



Much of our future supply of oil will be found by close teamwork between 

 various oil-finding groups, utilizing all of our present known prospecting tools 

 and exploration methods. To a great extent this effort will consist of detailed 

 subsurface studies in the search for stratigraphic traps and accumulations on 

 the flanks and extensions of known structures; and deeper drilling wherever 

 possible. There are, however, some rather extensive areas having good oil pos- 

 sibilities but about which we know very little because of a cover which masks 

 the underlying geological conditions and which we cannot effectively penetrate 

 with any of our present methods because of physical or economic considerations. 



These masks include overthrust segments, blankets of young vol- 

 canics, thick alluvial and glacial deposits, multiple unconformities, and 

 even water, which covers favorable stratigraphic and structural condi- 

 tions on the continental shelves. Noble points out the oil and gas possi- 

 bilities underlying the thrust sheets, as at Turner Valley in western Alberta, 

 and similar conditions in Montana and the Pacific Coast and Midcontinent 



^Cheney, M. G., The Geological Attack: Am. Assoc. Petroleum Geologists Bull., vol. 30, no. 7, 

 pp. 1079-1080, July 1946. 



^ Noble, E. B., Geological Masks and Prejudices: Am. Assoc. Petroleum Geologists Bull., vol. 31, 

 no. 7, pp. 1109-1117, July 1947. 



