3-D transport and acoustic properties of Fontainebleau sandstone during true-triaxial deformation experiments

摘要

Fontainebleau sandstone specimens have been tested in a true-triaxial geophysical imaging cell under hydrostatic (σ_1 = σ_2 = σ_3), traditional triaxial (σ_1 =σ_2 >σ_3) and true-triaxial (σ_1 > σ_2 >σ_3) stress regimes. The research objectives are to recognize the effect of various stress ratios σ_2/σ_3 under varying magnitudes of σ_2 and σ_3 on 3-D stress-strain responses, 3-D transport, 3-D ultrasonic wave velocities, and acoustic emission properties. Comparison of the variation of 3-D directional permeability between the specimens shows that higher magnitude of σ_3 and σ_2 disrupts the 3-D interconnectivity of the pore spaces and intergranular cracks, irrespective of the magnitude of applied stress ratio σ_2lσ_3. The observed permeability anisotropy between the two specimens is a function of inherent oriented pores and cracks, stress ratio σ_2/σ_3 and the magnitude of applied σ_3 and σ_2 stresses. Temporal and spatial evolution of the AE hypocenter locations combined with the examination of micro-CT and thin section images shows the timely development of polymodal fault systems during peak to post-peak stresses and validates the development of the source mechanism inferred from the acoustic emission events.