Early geophysical papers of the Early geophysical papers of the Society of Exploration Geophysicists earlygeophysical00soci Year: 1947 148 C. A. H EI LAND ness of 400 feet underlain by salt. The resistance of the gypsum is high, and that of the shales is low. Where the effect of the salt has been picked up, its resistance seems to be fairly low, such as shown in well No. 48, which is somewhat contrary to the experience obtained on salt domes. AIL resistivity traverses shown in Figure 31 have a simi- lar appearance as far as the very high resistance surface layers are con- Fig. 32.—Results
Early geophysical papers of the Early geophysical papers of the Society of Exploration Geophysicists earlygeophysical00soci Year: 1947 148 C. A. H EI LAND ness of 400 feet underlain by salt. The resistance of the gypsum is high, and that of the shales is low. Where the effect of the salt has been picked up, its resistance seems to be fairly low, such as shown in well No. 48, which is somewhat contrary to the experience obtained on salt domes. AIL resistivity traverses shown in Figure 31 have a simi- lar appearance as far as the very high resistance surface layers are con- Fig. 32.—Results of electrical vertical drilling using single-probe method (Ilfl) and corresponding well log at Berthoud dome, Colorado. (Measurements made by Keen, Bishop, and Johnson.) cerned. Then they all show a pronounced 'low,' corresponding with the influence of the red beds and shales close to the surface. After that, all curves go up again, depending on the amount of gypsum present in the section. Thus, while the curves of Nos. 45 and 46 are practically flat, they are steeper in 49, 44, 43, and steepest in 48. Just what takes place in No. 48 is not very well known on account of lack of knowledge of the well log; but it seems that the formations present at that local- ity, probably gypsum, are very poor conductors. A striking similarity 478
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