HR: 0800h
AN: H11E-0335    [Abstracts]
TI: Acoustic Effects on Colloid/Surface Interactions and Porous-Media Permeability
AU: * Roberts, P M
EM: proberts@lanl.gov
AF: Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM 87545 United States
AU: Abdel-Fattah, A I
EM: amr2450@lanl.gov
AF: Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM 87545 United States
AU: Duran, J
AF: Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM 87545 United States
AB: Acoustic and seismic waves have been observed to influence porous fluid-flow behavior in the Earth and geomaterials over a wide range of scale lengths (microns to kilometers). Examples include oil reservoir production increases induced by seismic (1 to 500 Hz) waves, and mobilizing colloidal clays in sandstone cores by ultrasonic (10 to 50 kHz) energy. The effects of stress-wave propagation on both colloid electrokinetics and fluid-flow dynamics in porous media are not understood. In particular, the coupling of acoustic and seismic waves with colloid behavior is an important mechanism to understand because the distribution of colloids in a porous medium will directly affect its permeability. Recent experimental observations indicate that very-high-frequency (0.5 to 5 MHz) acoustic energy can induce attachment and detachment of micron-size colloids at solid surfaces. Using a microscopic, video image-processing system focused on a glass flow-visualization cell, the behavior of 0.5- to 3-micron diameter polystyrene spheres suspended in 0 to 0.1 M aqueous solution was observed. Initial image-processing-based analysis of acoustically-induced colloid/surface detachment events indicates that very-high-frequency acoustics not only increases particle detachment, but may also permanently "deactivate" colloid attachment (or "active") sites on the glass cell surface. The ability of acoustics to attach or detach colloids also appears to depend on the colloid size and ionic strength of the suspending solution. Other experiments show that seismic-band (1 to 1000 Hz) mechanical stress oscillations can change the permeability of centimeter-size sandstone cores due to mobilization of micron-size colloids contained in the pore space. A unique core-holder apparatus that mechanically strains 2.54-cm-diameter porous rock samples during constant-rate fluid flow was used for these experiments. During single-phase brine flow through sandstone, axial stress oscillations at 50 Hz mobilized in-situ clay colloids and increased the absolute permeability of the rock by 10 to 20 percent. New experiments are being performed by injecting into clean core samples the same polystyrene colloid suspensions used in the microscopic visualization experiments. Observations of both micro- and core-scale behavior will be presented and discussed.
DE: 5114 Permeability and porosity
DE: 5139 Transport properties
DE: 1899 General or miscellaneous
DE: 1829 Groundwater hydrology
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting