engleski

Application of IP method for discovering clay zones in carbonate terrains

Induced polarisation (IP) method can be very interesting in hydrogeological explorations in karst terrains. In such terrains water can usually be find in faulted and fractured zones that are showing significantly lower resistivities than the compact rock. Similar decrease of resistivity can occur due to a presence of clay in fractured carbonate zones. Besides resistivity increase, clays can also show IP anomalies and therefore it is theoretically possible to distinguish fractured zones with water from fractured zones with clay. Resistivity and IP measurements were carried out on two profiles set out in Manojlović vrelo near town Ogulin and in Velika Jamnička near Zagreb. Manojlović vrelo is situated in karst terrain and Velika Jamnička in aluvial terrain. Manojlović vrelo profile showed low values of chargeabilities (0-5 ms), and there were no IP anomalies on this profile. In the central part of resistivity profile there were low resistivities that indicated the presence of fractured zone. This fractured zone could be filled with water or with clay. The values of chargeability were not increased in this part of profile and therefore it was concluded that the fractured zone was filled with water. On the Velika Jamnička profile very high values of chargeability were discovered (more than 50 ms). These anomalies generally match with zones of low resitivities in resistivity profile on this location and indicate the presence of clay sediments. Measurement results on these two examples indicate that zones with water can be distinguished from clay zones using combined application of IP method and resistivity method.

induced polarization; resistivity; hydrogeology; karst

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