5:15 PM - 6:30 PM
[SCG50-P11] Electrical conductivity in a brine-saturated granite under uni-axial compression
Keywords:electrical conductivity, crack, fluid, stress
Measurements of elastic wave velocity and electrical conductivity have been made on a brine-saturated rock (Aji granite) under uni-axial compression (< 20 MPa) in order to understand the influence of differential stress on electrical conductivity in fluid-bearing rocks. Microcracks perpendicular to the compression axis were preferentially closed to show anisotropic change in elastic wave velocity. Velocity significantly increased in the direction parallel to the compression axis, while it showed little change in the direction perpendicular to the compression axis. On the contrary, electrical conductivity showed no anisotropic change: conductivity decreased similarly in directions parallel and perpendicular to the compression axis. Cracks perpendicular to the compression axis, which were closed under compression, must contribute to electrical conduction in directions parallel and perpendicular to the compression axis. In order to understand the observed change in conductivity, the orientation distribution of cracks must be evaluated.
The orientation distribution of cracks can be evaluated by the crack density tenor (e.g., Sayers and Kachanov., 1995), which is calculated from elastic compliance tenor. In order to determine full compliance tensor, velocity must be measured in a direction oblique to the sample surface. Velocity measurement at an oblique angle was successfully made by attaching small (~10 mm) Aji granite prisms on sample surfaces. In a preliminary experiment on the dry sample, crack density tensor showed the closure of cracks perpendicular to the compression axis. We will next determine crack density tensor and aspect ratio in the wet sample and construct a quantitative model of electrical conduction to reproduce the observed conductivity change in both directions.
The orientation distribution of cracks can be evaluated by the crack density tenor (e.g., Sayers and Kachanov., 1995), which is calculated from elastic compliance tenor. In order to determine full compliance tensor, velocity must be measured in a direction oblique to the sample surface. Velocity measurement at an oblique angle was successfully made by attaching small (~10 mm) Aji granite prisms on sample surfaces. In a preliminary experiment on the dry sample, crack density tensor showed the closure of cracks perpendicular to the compression axis. We will next determine crack density tensor and aspect ratio in the wet sample and construct a quantitative model of electrical conduction to reproduce the observed conductivity change in both directions.