  Recent progress in extraction of unconventional hydrocarbon resources has
ignited the interest in the studies of nanoporous media. Since many
thermodynamic and mechanical properties of nanoscale solids and fluids differ
from the analogous bulk materials, it is not obvious whether wave propagation
in nanoporous media can be described using the same framework as in macroporous
media. Here we test the validity of Gassmann equation using two published sets
of ultrasonic measurements for a model nanoporous medium, Vycor glass,
saturated with two different fluids, argon and n-hexane. Predictions of the
Gassmann theory depend on the bulk and shear moduli of the dry samples, which
are known from ultrasonic measurements, and the bulk moduli of the solid and
fluid constituents. The solid bulk modulus can be estimated from
adsorption-induced deformation or from elastic effective medium theory. The
fluid modulus can be calculated according to the Tait-Murnaghan equation at the
solvation pressure in the pore. Substitution of these parameters into the
Gassmann equation provides predictions consistent with measured data. Our
findings set up a theoretical framework for investigation of fluid-saturated
nanoporous media using ultrasonic elastic wave propagation.
