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3-D converted shear wave rotation with layer stripping

  • US 5,610,875 A
  • Filed: 09/29/1995
  • Issued: 03/11/1997
  • Est. Priority Date: 09/29/1995
  • Status: Expired due to Term
First Claim
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1. A method for defining the geographic orientation of the principal axes of a birefringent medium for use in selecting the direction of deviation of a horizontal borehole relative to the strike of a lithologic fracture plane, comprising:

  • radiating a compressional wavefield from a first source location;

    from a first receiver station spaced apart from said first source location along a first azimuth, detecting first and second seismic signal components representative of fast and slow converted shear-wave energy reflected from a subsurface conversion point associated with an acoustic interface beneath a birefringent medium;

    radiating a compressional wavefield from a second source location;

    from a second receiver station spaced apart from said second source location along a second azimuth substantially perpendicular to said first azimuth, detecting third and fourth signal components representative of fast and slow converted shear-wave energy reflected from said subsurface conversion point;

    programming a digital computer to format said first, second, third, and fourth signal components into a 2×

    2 matrix, said matrix including diagonal and off diagonal terms;

    with the aid of said computer, applying a four-term rotation operator to said matrix which minimizes the energy content of the off-diagonal terms of said matrix to define the orientation of the principal polarization axes of said birefringent medium as the fracture-plane strike; and

    deviating a borehole perpendicular to the so-defined strike.

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