Presenter: Yung-Chieh Chuang
Date: 2015/11/26
Abstract
The self-potential method is the only non-intrusive method that is directly sensitive to the flow of the pore water in a porous material. Exactly, the flow of the pore water drags the electrical charges located in diffuse layer, and therefore triggers the self-potential anomaly, known as streaming potential. In this presentation, first of all, the authors showed a laboratory test to demonstrate how the passage of a salt tracer affects the self-potential response. Then fit the positive self-potential anomaly by trial and error, and estimated the hydraulic permeability k equal to 7.2510-11m2 (the measured value is =(92)10-11m2), an excess of charge per unit pore volume equal to 0.13Cm-3 (the measured value is =0.110.02Cm-3). Second, they developed a sand box experiment showing that the self-potential method can locate both the source of leakage and the front of a contaminant plume. From the time-lapse self-potential inversion results and synthetic test, a positive volumetric source current density was associated with the position of leak at the bottom of the leaking tank, whereas a negative volumetric source current density was associated with the salinity front moving down inside the sandbox. Finally, they applied this new methodology to a field test site (a dam with a proven leakage) located in the south of France. Self-potential mapping was first performed to locate the preferential flow path. And from the time-lapse data, they estimated the hydraulic permeability in the leaking area k equal to (5)10-8m2.
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