Elastic wave propagation in saturated porous rocks reflects the fluid
and mineral stiffness and their frequency-dependent interaction. Seismic imaging and borehole
measurements in the field use low-frequency, long-wavelength signals (Hz-to-kHz),
while standard laboratory-measurements operate in the MHz range. This thesis
advances broadband elastic wave propagation methods (quasi-static, cyclic loading,
first-mode resonance, and ultrasonic) to characterize intact rocks in order to gather
laboratory data relevant to field conditions.
Results show the critical effect of surface roughness at the specimen-endcap
interfaces on stiffness measured under quasi-static conditions; local strain
measurements using specimen-bonded strain gauges avoid seating effects.
Multi-mode low-frequency resonant column testing provides the most reliable
assessment of attenuation; attenuation increases and resonant frequency decreases
with vibration amplitude for all vibration modes (longitudinal, torsional, and
flexural). Ultrasonic P and S-wave velocities increase as a function of conf fining
pressure and during early stages of deviatoric loading; trends follow a Hertzian
power law. The corresponding -factors and -exponents exhibit a strong
correlation with specimen type. The combination of ultrasonic measurement and
coda wave analysis allows us to detect minute velocity changes during
fluid invasion
and damage evolution. Differences in P-wave velocity in specimens saturated with
brine and supercritical CO2 are higher at seismic frequencies than in ultrasonic
frequencies.
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The new experimental methods implemented in this research and the
comprehensive characterization studies provide new tools into intact rock
characterization and contribute new insights on the physical properties of intact
rocks and
fluid-matrix interaction. Results highlight critical differences between
field values and standard laboratory measurements
| Date of Award | Apr 2021 |
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| Original language | English (US) |
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| Awarding Institution | - Physical Sciences and Engineering
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| Supervisor | J. Carlos Santamarina (Supervisor) |
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