ADVANCES IN TECHNIQUE AND APPLICATION OF 
RESISTIVITY AND POTENTIAL-DROP-RATIO 
METHODS IN OIL PROSPECTING! 
C. A. HEILAND? 
Golden, Colorado 
ABSTRACT 
The successes which have been obtained with electrical methods of prospecting in 
detecting metallic ore bodies have led to repeated attempts to use them also in oil 
prospecting, both in structural work and in locating the oil itself. These attempts have 
not met with as much success as the application of electrical methods to the location 
of ore bodies; however, the interest in the possibilities of electrical prospecting as ap- 
plied in oil work has been aroused again of late, due to the perfection of the resistivity 
and potential-drop-ratio method in regard to the determination of the depth to geologic 
bodies. 
The object of the writer is to give a summary of the whole field of the resistivity 
methods, with particular reference to the recent developments. The factors affecting 
the resistivity of rocks, and methods for the determination of resistivities of rocks and 
formations are described. Then follows a description of the various surface-potential 
methods. First, the resistivity methods proper are discussed, with reference to electrode 
arrangement, apparatus, and methods of interpretation used. Second, the potential- 
drop-ratio methods are treated, also with regard to the electrode arrangements, ap- 
paratus, and methods of interpretation. The opinions of various authors are discussed 
who have expressed their views about the possibilities of locating oil directly by elec- 
trical methods, and examples are presented of results which have been obtained thus 
far with resistivity methods, both in structural prospecting and in attempting to locate 
the oil directly. 
A. PRINCIPLES AND HIsToRY OF RESISTIVITY PROSPECTING 
In prospecting for oil structure, the four major geophysical 
methods—gravitational, magnetic, seismic, and electrical—have been 
widely used. Both the seismic and electrical methods have a distinct 
advantage over the gravitational and magnetic methods: the possi- 
bility of controlling the depth of penetration. This is an important 
factor in the interpretation of the results, as not only the physical 
characteristics but also the depths of geologic formations are ob- 
tained. 
Thus, the seismic and electrical methods as applied in oil prospect- 
ing have a number of features in common; on the other hand, they 
1 Read before the Association of the Oklahoma City meeting, March 25, 1932- 
(Series of publications No. 43, Dept. of Geophysics, Colorado School of Mines. 
2 Professor of geophysics, Colorado School of Mines. 
go 
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