HR: 0800h
AN: S41A-0930    [Abstracts]
TI: Acoustic Emissions, Velocities And Permeability Evolution During Formation Of Compaction Bands In Sandstone.
AU: * Fortin, J
EM: fortin@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24, rue Lhomond, Paris, 75005 France
AU: Stanchits, S
EM: stanch@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg D425, Potsdam, 14473 Germany
AU: Dresen, G
EM: dre@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg D425, Potsdam, 14473 Germany
AU: Schubnel, A
EM: alexandre.schubnel@utoronto.ca
AF: Lassonde Institute, University of Toronto, 170 College street, Toronto, ON M5S 3E3 Canada
AU: Gueguen, Y
EM: gueguen@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure, 24, rue Lhomond, Paris, 75005 France
AB: Compaction bands are zones of localized deformation observed in high porosity rock (Mollema et al. [1996], Klein et al. [2001], Fortin et al. [2003]). These planar bands form perpendicular to the direction of maximum compression. Compaction bands display significantly reduced porosity and are potentially important permeability barriers in reservoir rocks and aquifers. To investigate localized compaction and changes in physical properties of porous sandstone, we performed triaxial tests on Bleurswiller sandstone, (50% quartz 30% feldspars and 20% clay, 25% porosity), on Fontainebleau sandstone (100% quartz, 25% porosity) and on Flechtingen sandstone (65-75% quartz, calcite and illite 15%, porosity 5.5-7%). Experiments were performed under wet conditions at a pore pressure of 10 MPa. Thirteen experiments were performed at the Laboratoire de Geologie (Ecole Normal Superieur Paris) and at GeoForschungsZentrum Potsdam. Evolution of volumetric strain, elastic wave velocities and permeability were recorded at confining pressures of 12 and 180 MPa. Acoustic Emission (AE) characteristics during deformation were studied at GeoForschungsZentrum Potsdam. To monitor velocity change and microcracking of sandstone, 10 P-wave sensors and 8 polarized S-wave piezoelectric sensors were glued to the cylindrical surface of the samples. To monitor fracture-induced anisotropy, two additional P sensors were installed in axial direction. Fully digitized waveforms were recorded by 10 MHz/16bit Data Acquisition System with an accuracy of AE hypocenters determination of about 2.5 mm. Location of acoustic emission events reveal the evolution of localized compaction bands in sandstone subjected to axial compression. The formation of the bands depends on rock type and effective pressure. Our experiments show a reduction of permeability across compaction bands by about one to two orders of magnitude (Vajdova et al. [2004]; Holcomb et al., [2003]) suggesting that the bands may act as barriers to fluid flow in porous rocks. Samples were first subjected to increasing confining pressure and subsequently loaded axially. During hydrostatic compression, elastic wave velocities first increased up to 10% due to crack closure and compaction. After onset of axial loading, transverse velocities decreased by 10%-20% owing to induced crack damage and depending on rock type and confining pressure. Axial velocity component first increased slightly with increasing mean stress and dropped to starting value.
DE: 5102 Acoustic properties
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 5114 Permeability and porosity
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting