| Summary: | Laboratory measurements of ultrasonic p- and S-wave velocities were made as
a function of confining pressure for vacuum dry, benzene-, and water-saturated
samples of Westerly granite, Bedford limestone, and Weber, Navajo, Berea, and
Kayenta sandstones. The measurements indicate: 1) water-saturated bulk moduli are
higher than benzene-saturated values, 2) fluid-saturated shear moduli are always
greater than or equal to dry values, and 3) water-saturated shear moduli for the
sandstones are higher than benzene values at low pressure while lower than both
benzene and dry values at higher pressure, Indicating that an apparent water-softening
effect Is concentrated In the shear modulus. Modelling of the velocity
measurements with the Blot (1956a) and Gassmann (1951) equations for static
effective bulk modulus indicates that it underestimates the increase in bulk modulus
and velocities caused by fluid saturation. Inertial effects of the pore fluid as treated
by Blot (1956a, 1956b) are also shown to give minimal improvement to predicted
velocities, which are underestimated. Velocity measurements are modelled with the
Cheng-Kuster-Toksoz ellipsoidal pore and crack model using the inversion technique
developed by Cheng (1978). Fits of dry and benzene-saturated velocities are shown
along with pore aspect ratio distributions at zero pressure. Water-saturated velocity
data and measured porosity reductions with pressure are compared with predictions
of the model.
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