Early geophysical papers of the Early geophysical papers of the Society of Exploration Geophysicists . earlygeophysical00soci Year: 1947 10 L. J. PETERS AND J. BARDEEN covers a thick sediment with a large change in resistivity. Then the contours will roughly approximate the topographical contours on the sediment. Sup- pose that the sediment has a low resistivity. Then when it is near the surface, the apparent resistivity will be low. When the sediment is deeper, the ap- parent resistivity will be higher. The apparent resistivity map, of course, gives only a qualitative inter- pretation of the
Early geophysical papers of the Early geophysical papers of the Society of Exploration Geophysicists . earlygeophysical00soci Year: 1947 10 L. J. PETERS AND J. BARDEEN covers a thick sediment with a large change in resistivity. Then the contours will roughly approximate the topographical contours on the sediment. Sup- pose that the sediment has a low resistivity. Then when it is near the surface, the apparent resistivity will be low. When the sediment is deeper, the ap- parent resistivity will be higher. The apparent resistivity map, of course, gives only a qualitative inter- pretation of the electrical data. The methods at present in use for interpret- ing Cish-Rooney surveys give only approximate depths to the points at which sharp changes occur in the resistivity of the earth. These approxima- Fig- 6. Qualitative interpretation of Gish-Rooney survey shown in Fig. 5, giving correlation with core drill. tions become worse and worse as the number of resistivity contrasts become greater. A rigorous solution of the problem of finding the variation of re- sistivity with depth from surface potential measurements under the assump- tion that the resistivity is substantially a function of the depth only could be based upon solutions of the potential problem given by the theory of images. However, these solutions are cumbersome to handle when the number of layers which must be dealt with exceeds two. The integral solution given in this paper is much easier to handle in the case of multilayer problems and should aid in placing the interpretation of direct current surveys on a more exact basis. III. Electromagnetic Methods Electromagnetic methods depend primarily on the induction of currents in the earth by means of a primary current on the surface. Inhomogeneities in the earth will affect the resultant field on the surface. In oil prospecting these inhomogeneities take the form of practically horizontal beds with different conductivities. Many different schemes have been
Size: 3654px × 547px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
