ADVANCES IN OIL PROSPECTING 159 
Koenigsberger has published results obtained along three potential- 
drop-ratio traverses in the Oberg field in Germany, of which only the 
ones measured on the extreme west and the ones measured on the 
extreme east side of the field lend themselves to graphical representa- 
tion. The location of these traverses is shown in Figure 4o a. By 
designating with Koenigsberger the interval between the power 
electrodes by 2a, results are available in this author’s publications 
for intervals a equal to 100, 200, and 300 meters for the southern 
part, and for the intervals of 50, 100, and 200 meters for the northern 
part of the traverse on the west side of the field, while the distances 
used were 50, 100, and 200 meters in both traverses on the east side 
of the oil field. The productive zone is located on the west side of the 
area, and the oil is taken from a depth of approximately 300 meters 
from strata of the lower part of the middle Jurassic, while in the 
central part of this area the productive zone is nearly 500 meters in 
depth. At the locality at which the eastern traverses were made, the 
lower Dogger strata presumably contain salt water instead of oil. 
From the foregoing figures for the distances used, it is seen that 
potential-drop ratios are given only for four (or three, respectively) 
depths in the western and for three depths in either traverse on the 
east. Koenigsberger states in his publication that the depth corre- 
sponding with the potential-drop-ratio indications is h=14a, and the 
observed potential-drop-ratio values have been plotted in the middle 
part of Figure 40 in accordance with this depth rule. As for normal 
_ ground the ratio is 3.57, values greater than this ratio have been 
plotted at the right, values smaller than this value were plotted at the 
left. As seen from Figure 40 ¢, the indications obtained from poor 
conductors are not nearly as pronounced as the indications from good 
conductors below; in order to equalize the indications somewhat, the 
logarithmic scale was employed to draw the curves shown in Figure 
40 b. 
Koenigsberger, in his article, now makes the statement that ‘“‘the 
influence of insulating formations is quite evident from the fact that 
the ratio drops below 3.6 in the traverse on the west side.” 
_ The writer does not see how the observed values can possibly be 
correlated with the productive area, as the electrode spacing used 
was in all cases too small to penetrate down to the oil-bearing forma- 
tions. On the other hand, it is true that some oil occurs in this field 
above the productive zone in the strata of the lower Dogger (that is, 
in depths less than 300 meters) and it is also possible that the diffusion 
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