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Multiple depths and frequencies for simultaneous inversion of electromagnetic borehole measurements

  • US 5,469,062 A
  • Filed: 03/11/1994
  • Issued: 11/21/1995
  • Est. Priority Date: 03/11/1994
  • Status: Expired due to Term
First Claim
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1. A wave propagation method for measuring electromagnetic properties of earth formation penetrated by a borehole and simultaneously correcting said measurements for the adverse effects of drilling fluid invasion and bed boundary conditions, comprising:

  • (a) providing a borehole instrument comprising at least two transmitter-receiver pairs;

    (b) operating each said transmitter at a first operating frequency and at a second operating frequency thereby inducing electromagnetic radiation within the borehole and formation environs at each operating frequency;

    (c) measuring the amplitude and phase of electromagnetic radiation detected by the receiver component of each said transmitter-receiver pair and computing values of apparent resistivity, at each said operating frequency, from the ratios of said amplitude measurements from each receiver pair, and from the differences of said phase measurements from each said receiver pair;

    (d) providing a model of the response of said borehole instrument which relates said apparent resistivity measurements to a plurality of formation and borehole parameters representative of the environs in which said borehole instrument is expected to operate, and wherein said model is obtained from apparent resistivity determinations made with said borehole instrument operating in environs of known formation and borehole parameters;

    (e) selecting, from said plurality of formation and borehole parameters, parameters of interest to be determined;

    (f) mathematically combining said apparent resistivity measurements with said instrument response model to compute said parameters of interest and simultaneously correct said parameters of interest for the adverse effects of formation bed boundary and borehole perturbation effects; and

    (g) repeating (b) through (f) as said borehole instrument is conveyed along the borehole.

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