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Sonic well logging for alteration detection

  • US 6,526,354 B2
  • Filed: 02/01/2001
  • Issued: 02/25/2003
  • Est. Priority Date: 02/01/2001
  • Status: Expired due to Term
First Claim
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1. A method for determining alteration of a region of an earth formation surrounding an earth borehole, comprising the steps of:

  • providing a logging device that is moveable through the borehole;

    transmitting sonic energy into the formation and receiving, at a plurality of transmitter-to-receiver spacings on said logging device, sonic energy that has traveled through the formation, and producing signals representative of the received sonic energy for said plurality of transmitter-to-receiver spacings;

    determining, from said signals, sonic transit times and differential transit times for the respective transmitter-to-receiver spacings;

    deriving a test statistic from said differential transit times; and

    determining the presence of alteration of a region of the formations from said test statistic.

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