HR: 17:30h
AN: MR24A-07    [Abstracts]
TI: Pore Space Geometry and Seismic Anisotropy of Rocks: 3-D Experimental Investigation
AU: * Spacek, P
EM: spacek@ipe.muni.cz
AF: Geophysical Institute, CAS, Bocni II/1401, Prague, 141 31 Czech Republic
AU: * Spacek, P
EM: spacek@ipe.muni.cz
AF: Institute of Earth Physics, Masaryk University, Tvrdeho 12, Brno, 602 00 Czech Republic
AU: Melichar, R
EM: melda@sci.muni.cz
AF: Department of Geosciences, Masaryk University, Kotlarska 2, Brno, 602 00 Czech Republic
AU: Ulrich, S
EM: stano@ig.cas.cz
AF: Department of Petrology and Structural Geology, Charles University, Albertov 6, Prague, 128 43 Czech Republic
AB: Pressure-driven closing of the pores in the rock sample results in changes of its effective physical properties. We use 3-D ultrasonic pulse-transmission method to characterize the relationships between the spatial distribution of microcracks and elastic anisotropy of the rock. With the use of apparatus developed in Geophysical Institute, Prague, the P-wave velocities and amplitudes ({\IT V$_{P}$} and {\IT A$_{P}$}) are measured in 132 directions on spherical rock samples. The measurements are carried out at several steps of confining pressure within pressure-increasing and pressure-decreasing paths (0.1-400, 400-0.1 MPa). Then the directions of maximum and minimum velocities and amplitudes are found for which the measurements is repeated under continually changing pressure. As the measurements are repeated at the same position under various pressures, the data can be processed so that the change of the {\IT V$_{P}$} and {\IT A$_{P}$} between the individual pressure-steps and the hysteresis at particular pressure can be seen directly. The resulting differential diagrams show the magnitude of {\IT V$_{P}$} and {\IT A$_{P}$} changes in 3-D which are mainly due to the pressure-induced closing of microcracks, and respectively, the flexibility of the microcracks. Using the data measured at high confining pressure or those computed with averaging method we are able to distinguish the influence the deformation-induced lattice re-orientations from the pore-related properties. Numerous measurements carried out on various rock samples show that the anisotropic patterns of {\IT V$_{P}$} and {\IT A$_{P}$} changes due to the closing of oriented microcracks and other pores highly correlate with the macroscopic structural features of the rock (preferred grain-shape orientation, fracture cleavage, stretching lineation) and are sensitive to them. It is believed that in such cases where the structural features associated with porosity can not be observed directly, the above outlined method will be applicable as a tool for the examination of pore space geometry.
DE: 7203 Body wave propagation
DE: 3904 Defects
DE: 3909 Elasticity and anelasticity
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting