Extensional wave attenuation and velocity in partially-saturated sand in the sonic frequency range
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Extensional wave attenuation and velocity in partially-saturated sand in the sonic frequency range

  • Author(s): Liu, Z.
  • Rector, J.W.
  • Nihei, K.T.
  • Tomutsa, L.
  • Myer, L.R.
  • Nakagawa, S.
  • et al.
Abstract

Extensional wave attenuation and velocity measurements on a high permeability Monterey sand were performed over a range of gas saturations for imbibition and degassing conditions. These measurements were conducted using extensional wave pulse propagation and resonance over a 1 - 9 kHz frequency range for a hydrostatic confining pressure of 8.3 MPa. Analysis of the extensional wave data and the corresponding X-ray CT images of the gas saturation show strong attenuation resulting from the presence of the gas (QE dropped from 300 for the dry sand to 30 for the partially-saturated sand), with larger attenuation at a given saturation resulting from heterogeneous gas distributions. The extensional wave velocities are in agreement with Gassmann theory for the test with near-homogeneous gas saturation and with a patchy saturation model for the test with heterogeneous gas saturation. These results show that partially-saturated sands under moderate confining pressure can produce strong intrinsic attenuation for extensional waves.

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