Active and Passive Seismic Monitoring of Shales Under Triaxial Stress Conditions in the Laboratory

Laboratory experiments are reported that were aimed at estimating various rock physics parameters that are of importance in geophysics. Several triaxial deformation experiments on shale specimens from two offshore oil field reservoirs have been performed. Three main parameters were continuously monitored during the deformation process: (i) gas permeability; (ii) local strains in various directions; (iii) longitudinal and shear wave velocities for various directions of propagation; and (iv) micro-seismic events induced by the triaxial stress loading. The wave velocity surveys performed at various stages along the loading path allowed for the estimation and the update of the elastic wave velocity field. The strain data allowed for the update of the wave travel path length along the stress loading. This procedure ensured an accurate and reliable localization of the micro-seismic events that occurred between consecutive surveys. It also allowed for the estimation of the evolution of shale anisotropy under traixial stress loading.