SOME ASPECTS OF ELECTRICAL PROSPECTING 
APPLIED IN LOCATING OIL STRUCTURES 
By Leo J. Peters anp JoHN BARDEEN 
Tue Guur CompanigEs, RESEARCH DEPARTMENT, PITTSBURGH, Pa. 
(Received February 2, 1932) 
ABSTRACT 
Electrical prospecting is defined as the science and the art of determining the 
variations of the electrical constants (resistivity, magnetic permeability and the di- 
electric constant) of the earth’s crust and of interpreting these variations in terms of 
geological structure. The most successful systems of prospecting are based on the 
study of resistivity variations. The basic assumption made is that in general changes of 
resistivity follow the bedding planes. Electrical methods of exploration may be divided 
into two classes, direct current methods and alternating current methods. In part II 
the fundamental theory of direct current method is discussed and a typical survey is 
described. Part III deals with the theory of alternating current methods, with partic-. 
ular reference to the optimum frequency to be used. It is shown that in general very 
low frequencies are desirable. Two alternating current surveys made by the Swedish 
American Prospecting Corporation are briefly described. In the conclusion (part IV) 
some of the difficulties of electrical prospecting are discussed. The depth to which in- 
vestigations may be carried is limited. In the present stage of the art, it would take 
exceptionally favorable conditions to obtain reliable information much in excess of 
2,000 feet. However, it is stated that improvements in methods of interpretation and 
in field technique should give electrical methods a definite field of usefulness in pros- 
pecting for oil. 
I. InTRODUCTION 
LECTRICAL prospecting may be defined as the science and the art of 
determining the variations of the electrical constants of the earth’s 
crust and of interpreting these variations in terms of geological structure or in 
terms of mineralization of a region. The three electrical constants whose vari- 
ation may be determined are the resistivity, the magnetic permeability and 
the dielectric constant. 
The resistivities of earth materials vary from a fraction of an ohm-cm 
to 10!” ohms-cm. The materials having values below 100 ohms-cm are con- 
fined largely to mineral ores such as marcasite, galena, molybdenite, chal- 
copyrite and iron pyrite. In the study of oil structures the resistivities en- 
countered vary from 100 to 10!” ohms-cm. In the Texas Gulf Coast region 
the common variation is from 200 to 20,000 ohms: cm with the exception of 
rock salt of which the resistivity has a value of the order of 101”. 
The dielectric constant of earth materials has a value which ranges from 
1 to 10. The variation in magnetic permeability, except in rare cases, is 
negligible. 
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