Borehole electrical images provide detailed views of subsurface formations. These are interpreted as quasi-geological images in terms of stratigraphy, sedimentology, and structure. Quantitative measurements of dips and strikes of planar features are possible, as are analyses of pixel distributions in terms of heterogeneities. The precise quantitative use of the image data in petrophysics is, however, not possible because the data do not represent actual formation resistivity values. High-resolution laboratory measurements of electrical resistivity on core samples are possible and provide a link between core petrophysical measurements and the downhole images. The adaptation of conventional quantitative contact resistivity measurements provides detailed appraisal of slabbed core at a similar resolution to the downhole images. These resistivity images can be related to porosity and minipermeametry core data and in turn to variations in grain-pore characteristics. Separately, development of electromagnetic, noncontact induction enables rapid continuous measurement of the conductivity (resistivity) of whole core. The resolution is slightly less than that of downhole images but this approach provides the capability of logging large volumes of core inexpensively without specialist core preparation. Numerical modeling of downhole electrical images demonstrates further that the borehole images respond to fine-scale resistivity changes. This suggests that the quantitative resistivity core images can be related directly to the downhole images, allowing their inclusion in petrophysical analyses, particularly involving thin beds and small-scale heterogeneities.
Electrical Resistivity Core Imaging: A Petrophysical Link To Borehole Images
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Flint, P.C., Gunn, D.A., Harvey, P.K., Jackson, P.D., Lovell, M.A., and C.G. Williams. "Electrical Resistivity Core Imaging: A Petrophysical Link To Borehole Images." The Log Analyst 38 (1997): No Pagination Specified.
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