Electrical conductivity evolution of non-saturated carbonate rocks during deformation up to failure

We present electrical conductivity measurements (at a fixed frequency of 1kHz) performed on three directions on limestone samples from the quarry of Meriel, during uniaxial tests of deformation up to failure. Samples were saturated from 100% to 80% by drainage. The samples showed brittle fracture with Young’s modulus in the range 10-13 MPa. Formation factor (sample resistivity divided by water resistivity) values range between 2 and 4. In saturated conditions the electrical measurements reflect the initial rock compaction, followed by dilatancy due to new axial cracks formation and finally crack coalescence, fracture localization and failure. The conductivity increase is related to the crack porosity Φc which starts to increase at relatively low stress (31% of strength). The magnitude of the electrical conductivity variation is 1 4 % of the initial value. We show that when saturation is decreased the conductivity increase occurs earlier during the deformation process, from 68% to 17% of strength for 100% to 80% of water saturation respectively, so that the decrease in