- journal_title：Geophysics
- Contributor：Robert R. Stewart ; Nikolay Dyaur ; Bode Omoboya ; J. J. S. de Figueiredo ; Mark Willis ; Samik Sil
- Publisher：Society of Exploration Geophysicists
- Date：2013-01-01
- Format：text/html
- Language：en
- Identifier：10.1190/geo2012-0075.1
- journal_abbrev：Geophysics
- issn：0016-8033
- volume：78
- issue：1
- firstpage：D11
- section：Borehole Geophysics and Rock Properties
Many regions of subsurface interest are, or will be, fractured. Seismically characterizing these zones is a complicated but essential task for resource development. Physical modeling, using ultrasonic sources and receivers over scaled exploration targets, can play a useful role as an analog for reservoir imaging and assessment. We explored the anisotropic response of glass blocks containing internal fractures created by a novel laser-etching technique. We compared transmitted and reflected signals for P- and S-waves from fractured and unfractured zones in a suite of ultrasonic (1–5 MHz) experiments. The unaltered glass velocities have averages of mula" id="inline-formula-1">mathjax mml-math">mathjax-code"><mml:math display="inline"><mml:mrow><mml:mn>5804</mml:mn></mml:mrow></mml:math>mathjax-text">5804 and mula" id="inline-formula-2">mathjax mml-math">mathjax-code"><mml:math display="inline"><mml:mrow><mml:mn>3447</mml:mn><mml:mrow><mml:mo> </mml:mo></mml:mrow><mml:mrow><mml:mo> </mml:mo></mml:mrow><mml:mi mathvariant="normal">m</mml:mi><mml:mo>/</mml:mo><mml:mi mathvariant="normal">s</mml:mi></mml:mrow></mml:math>mathjax-text">3447 m/s for P- and S-waves, respectively (giving mula" id="inline-formula-3">mathjax mml-math">mathjax-code"><mml:math display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mrow><mml:mstyle mathvariant="normal"><mml:mrow><mml:mi mathvariant="normal">P</mml:mi></mml:mrow></mml:mstyle></mml:mrow></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mrow><mml:mstyle mathvariant="normal"><mml:mrow><mml:mi mathvariant="normal">S</mml:mi></mml:mrow></mml:mstyle></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>1.68</mml:mn></mml:mrow></mml:math>mathjax-text">VP/VS=1.68). The unfractured glass has a very high quality (Q) factor of over 500 for P-waves and S-waves. The fractured zones have a small (up to 1.5%) velocity decrease. Signals propagating through the fractured zone have diminished amplitudes and increased coda signatures. Reflection surveys (zero-offset and with variable polarizations) record significant scatter from the fractured zones. The fracture-scattered energy can be migrated to provide a sharper image. The glass specimens with laser-etched fractures display a rich anisotropic response, which can help inform field-scale imaging.