ABSTRACT:

We present the results of a pilot experiment aimed at inducing micro-seismic/acoustic emission activity within a large pre-sheared rock block (240 × 120 × 150 mm3) subjected to controlled effective vertical stress and fluid flow. Micro-seismicity/acoustic emission monitoring was used to assess the impact of changes in (i) the vertical effective stress applied to the pre-sheared rock (1 and 0.4 MPa), and (ii) the fluid injection pressure (0.1, 0.2 and 0.27 MPa). To this end, a total of 32 P-wave ultrasonic sensors were attached to the sample’s external surface. The results show that the injection pressure was associated with a cloud of AE events located in the vicinity of the pre-existing shear plane. The decomposition of the moment tensors associated with the recorded events shows the complexity of fracture network generated during the experiment, i.e. mixed tensile and shear modes. Furthermore, higher injection pressure seems to enhance fault transmissibility, probably due to additional micro-fracturing.

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