Effect of Heterogeneity of Permeability on Streaming Potential

The objective of this study is to evaluate the effect of the groundwater flow on the streaming potential (SP) distribution. The heterogeneity of the permeability and complex water infiltration and upwelling through the ground surface generally causes the change of groundwater flow and SP distribution. In order to investigate the relationship between the heterogeneity of permeability and the SP anomalies, we conducted the numerical simulations of the groundwater flow and SP. Our numerical results show a gentle increasing trend of SP with amplitude of 60mV (-30mv at the upstream and +30mV at the downstream). However, the high permeability anomaly generates SP anomalies with amplitude more than 20 mV just above the boundaries of heterogeneity. Meanwhile the low permeability anomaly causes a small anomaly with amplitude less than 10mV for our simulation model. This difference in the SP distribution is caused by the different flow paths around the anomaly of high or low permeability. We also simulated the groundwater flow and SP induced by rainfall. The inflow by rainfall raised the water table with about 5m. The total SP distribution increased from 60mV to 80mV according to the increase of the groundwater flow, but did not change the general trend. The SP anomalies of about 10mV appear at where the water table contacts the ground surface. In order to discuss whether we can� detect heterogeneity of the permeability using SP data, we apply the downward continuation to SP distribution. The locations of the peaks in the gradient of the downward continuation are similar with the sources of SP. These results suggest us a possibility to image the subsurface heterogeneities of permeability using SP distribution.