Abstract

An analog modeling program has been conducted to provide a suite of anomaly profiles for electromagnetic logging of drill holes passing through and near subsurface conductors. Bodies considered include a small but highly conductive sulfide analog, a larger body of moderate conductivity (representing conductive shale), and a composite of the smaller body embedded in the larger one. Logs were obtained at two frequencies, two body dips, and three background or country rock resistivities. Results indicate that semiquantitative estimates of the extent of intersected conductors or the distance to missed conductors of similar properties to those modeled can be made. The use of two or more field frequencies and the recording of in-phase and quadrature components are recommended as a guide to differentiating between good and poor conductors. Dip effects are subtle and may not easily be recognized in field data. A conductive host rock will modify the log of a given conductive body.

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