The Detection of Induced Polarization with a Transient Electromagnetic System

The study of two-dimensional TEM models consisting of a cylinder in a conductive host using measured rock properties show that TEM surveys are capable of detecting induced polarization (IP) effects. A case history showing a comparable type of response is presented. The IP effects manifest themselves in extreme cases as negatives in the response and in other cases as anomalously high apparent resistivities. The models used allow a study of the variation of responses produced by varying the Cole-Cole constant for the cylinder properties. The results suggest that the different parameters produced distinct effects in the response. If the rock properties reported in the literature are correct, it appears quite feasible to observe IP effects via TEM using an ungrounded system. There may also occur a set of negatives in the response of a cylinder which are associated with high-conductivity contrasts and geometrical effects. In the cases studied these two groups are readily distinguished. IP effects might be interpreted from a family of zero responses (when these occur), apparent resistivity/time sections or by stripping away the host rock response and comparison with a uniform polarizable ground. There is a great deal of geometrical information about the scattering body at early times our of reach of many contemporary instruments.