New Model For@Volumetric Strain Of Rocks Under High Differential Stress And Large Shear Displacement

Details New Model For@Volumetric Strain Of Rocks Under High Differential Stress And Large Shear Displacement New Model For@Volumetric Strain Of Rocks Under High Differential Stress And Large Shear Displacement

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmmr51a0952t&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #MR51A-0952

Physics

5100 Physical Properties Of Rocks, 5104 Fracture And Flow, 5112 Microstructure, 5114 Permeability And Porosity, 5139 Transport Properties

Scientific paper

In confined triaxial compression tests, most sedimentary rocks change their behavior from a brittle to a ductile regime with increasing confining pressure. With effective increasing confining pressure, the differential axial stress increases and axial differential stress-strain curves show a transition from strain softening to strain hardening, and volumetric strains show a transition from dilatancy to persistent compaction. To investigate precisely the inner structural changes in stressed Shirahama sandstone with increasing axial strain and confining pressure, we measured porosity changes by means of mercury injection porosimetry and a gas adsorption method. Shirahama sandstone samples were deformed under various confining pressures and pore pressures. Under low confining pressures, the specimen is characterized by the existence of a main fault and the deformation shows dominant dilatancy. Under higher confining pressure experiments, the specimen behaves with fully ductile deformation, and volumetric strains measured by displacement transducers and measured by a pore volume apparatus show persistent compaction throughout the experiment. The porosity data obtained by mercury injection porosimetry and the gas adsorption method support the porosity increase behavior. Macroscopically, the specimens show persistent compaction, but microscopically the total porosity increases with increasing confining pressure. This phenomenon is attributed to micro-cracks caused by grain crushing and to the small open spaces around the rock fragments caused by high degrees of compaction and large shear displacement. In addition, we have introduced micro focus X-ray CT witth high resolution of 10 micron to visualize and measure the microstructure in rocks. We can get three-dimensional data simultaneously in the intact and stressed sandstone, pore structures and grain boundaries are distinguished well, pore closure and grain movement also are recognized well with increasing confining pressure and pore pressure. Micro focus X-ray CT is rather effective tools to visualize and measure the microstructure in rocks.

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