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Apparatus and method for simultaneously logging an electrical characteristic of a well formation at more than one lateral distance from a borehole

  • US 4,122,387 A
  • Filed: 08/24/1977
  • Issued: 10/24/1978
  • Est. Priority Date: 08/24/1977
  • Status: Expired due to Term
First Claim
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1. A well logging apparatus for measuring electrical properties of a formation intersected by a well bore wherein the electrical properties of the formation at a shallow distance and a deep distance from the borehole are simultaneously measured for display, comprising:

  • an armored logging cable;

    a logging sonde connected to the logging cable and arranged for movement in a borehole for logging the formation adjacent said borehole;

    a first investigating guard electrode system on said sonde having guard electrodes for focusing current to flow through the formation at a first lateral distance from the borehole, and a first alpha ring between said guard electrodes for emitting said current into said formation;

    a second investigating guard electrode system on said sonde, longitudinally spaced from said first investigating guard electrode system having guard electrodes for focusing current to flow through the formation at a second distance from the borehole, and a second alpha ring between said guard electrodes for emitting said current into said formation;

    a first electrical current source means for supplying a first formation current to said first alpha ring;

    a second electrical current source means for supplying a second formation current to said second alpha ring;

    said first and second formation currents being emitted simultaneously from said first and second alpha rings;

    oscillator means for controlling both said first electrical current source means and said second electrical current source means for imparting the same frequency to both of said first and said second formation currents;

    a cable electrode on said armored logging cable and insulated from said logging cable for providing a current return for current emitted from the alpha ring of one of said investigating guard electrode systems; and

    wherein said armored logging cable provides a current return for current emitted from the alpha ring of the other of said investigating guard electrode systems and flowing in a path separate from the path of the current emitted from said one electrode system alpha ring.

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