Application of the Mise-à-la-Masse method to detect the bottom leakage of water reservoirs

Leakages of reservoirs are responsible for the loss of water resources and the spread of contaminants. We develop a methodology to detect leaks located at the bottom side of a reservoir with the minimally invasive mise-à-la-masse method, which involves the potential electrodes located at the ground surface around the reservoir and the current source and sink placed in and out of the reservoir, respectively. This method allows localizing the secondary current distribution associated with leakage using the distribution of potential recorded on a set of electrodes during the mise-à-la-masse experiment. An initial model based on the distribution of root mean square values between the observation and the simulation data is first given to the inversion algorithm. The Tikhonov regularization, which includes a weighting matrix and a minimum support function, is used to strengthen the detection resolution of the leak. 29 sandbox experiments show that the proposed method and inversion algorithm can localize a single leak. For a leak with a crack shape, the inversion algorithm detects the location of the leak with a small bias. When the leak lasts, a conductive zone may occur below the leak due to the increase of water content or ionic strength of the pore water. The occurrence of such a conductive body could affect the localization of the leak because the conductivity distribution may not be well-resolved. The effect is analyzed using synthetic experiments. The results show that the bias between the real leak and inversion results increases with the position and size of the undetected conductive zone. Two small-scale field tests were conducted to test the performance of the mise-à-la-masse method. The two leaks are properly identified. This study provides an efficient approach to detect the bottom leakage of reservoirs.