APPLICATION OF INVERSE FILTERS TO INDUCTION LOG ANALYSIS

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Abstract
The general availability of digital computing equipment has motivated the investigation of the application of filtering techniques of communication theory to the analysis of electric and induction well logs. It will be shown that, with certain assumptions, the induction log may be represented as a linear filter with an impulse response and system function. A response equalization filter, which filters a shallow investigation log for comparison with a deep investigation log, may be used to scan pairs of induction, or induction and electric logs to detect invaded formations. An iterative process may be used to obtain an approximate solution for the depth of invasion from three appropriately chosen logs. Inverse convolution filtering may be used to obtain approximate resistivity values from apparent resistivity values indicated by the logs in radial zones concentric with the borehole for induction logs with different coil spacings.

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