HR: 0800h
AN: MR31C-0527    [Abstracts]
TI: Dispersion of Bulk Modulus of Partially-Saturated Porous Media
AU: * Dralus, D E
EM: dralus@stanford.edu
AF: Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AU: Wang, H F
EM: wang@geology.wisc.edu
AF: University of Wisconsin - Madison, 1215 W Dayton St, Madison, WI 53706, United States
AB: The elastic properties of partially-saturated porous media lie somewhere between a volume average of drained and undrained properties in the high frequency limit, and drained behavior in the low-frequency limit. The frequency dependence is related to the distribution of cluster sizes of the wetting fluid and the permeability. Johnson (2001) developed an approximation to Biot theory to predict the frequency dependence of the dynamic bulk modulus, which requires a solution to a Poisson equation of an auxiliary function over the saturated regions. To apply this theory, a coupled percolation-continuum evaporative drying model was used to produce simulated tomographic images of water distributions in a porous medium. The auxiliary function was then calculated using a finite difference method in order to calculate the full frequency spectrum of the bulk modulus of the patchy- saturated medium. The elastic moduli were then compared to those calculated from velocity data measured ultrasonically as a function of saturation for Massillon, Spirit River, and Schuler-Cotton Valley sandstone samples. Predictions from a heuristic model for determining elastic moduli, one that utilizes a Voigt volume average of the elastic properties along with the ad hoc rule that water-filled cells on the air-water interface behave in a drained manner, have already been shown to mimic the experimental data. The parameters found using the heuristic model were compared to those from the frequency-dependent bulk modulus calculations since the specific surface area arises naturally as a key geometrical parameter in both.
DE: 5199 General or miscellaneous
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting