Electrical images of the borehole wall are used in the investigation of fine-scale structures in a variety of applications including sedimentary, fracture. and petrophysical analyses. The wealth of high-resolution information in these images provides a means of performing detailed analyses in three dimensions in the vicinity of the borehole. However, it is easy to overlook anomalics and aberrations that may be caused by the tool measurement or borehole conditions. A numerical model has been developed in order to better understand electrical imaging measurements. The model simulates the current flow generated by a generalized electrical imaging device while located in formations with arbitrary three-dimensional (3D) resistivity properties. Interpretation of Formation MicroScanner2 data from a variety of sedimentary features is aided by comparison with specifically designed numerical simulations. Different models provide evidence for causes of anomalous images in response to small isolated conductive and resistive features and to conductive features that vary in their extent away from the borehole. The models also illustrate the depth of investigation of electrical images. which is typically less than 30 mm. Replication of known artifacts such as "halos" associated with thin dipping resistive layers confirms the validity of the numerical approach. As electrical image interpretation becomes increasingly sophisticated it remains imperative to appreciate the tool measurement process and the bearing this has on resultant images. The results given in this paper provide insight into the way the tool behaves in certain environments and evidence for specific anomalies that may be encountered. pointing to improved interpretation of sedimentary features.
Assessment And Interpretation Of Electrical Borehole Images Using Numerical Simulations
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Harvey, P.K., Jackson, P.D., Lovell, M.A., and C.G. Williams. "Assessment And Interpretation Of Electrical Borehole Images Using Numerical Simulations." The Log Analyst 38 (1997): No Pagination Specified.
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