HR: 1340h
AN: MR33A-0156    [Abstracts]
TI: Porosity Increase Behavior in Persistent Compaction Regime of Stressed Sandstone
AU: * Takahashi, M
EM: takahashi-gonsuke@aist.go.jp
AF: National Institute of Advanced Industrial Science and Technology, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki, 305-8567 Japan
AB: In confined triaxial compression test, most of sedimentary rocks behaved drastically from brittle to ductile with increasing confining pressure. With the effective confining pressure (defined as the confining pressure minus pore pressure) increasing, the differential axial stress increased and axial differential stress-strain curves show a transition from strain softening to strain hardening, and volumetric strain show a transition from dilatancy to persistent compaction. To investigate precisely inner structural change in the stressed sandstone with increasing axial strain and confining pressure, we made measurement of stress induced volume change by means of mercury injection porosimetry and gas adsorption method. 5 Shirahama sandstone were deformed under 0, 30, 50, 70, 90MPa of confining pressure in confined triaxial compression test. Under lower confining pressure, specimen was characterized by the existence of a main fault, the deformation showed dominant dilatancy. Under higher confining pressure experiment, specimen behaved fully ductile deformation, and volumetric strain measured by displacement transducers mounted on the specimen surface showed persistent compaction throughout the experiment. However, we confirmed that the porosity after experiment increased with increasing confining pressure. The porosity data obtained by the mercury injection porosimetry and gas adsorption method are supporting the experimental results. In macroscopic, specimen showed persistent compaction, but in microscopic stress induced porosity increased with increment of confining pressure. This phenomenon is attributed to the newly shear displacement enhanced cracks which occurs at the grain boundary and in the rock fragments.
UR: http://www.agu.org
DE: 1859 Rocks: physical properties
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005