Among the several types of induced polarization effects, electro-osmosis and membrane polarization by constrictivity of pores my result in non-linear behaviour, i.e. chargeability is not constant with supplied dc current. A new model, based on the second Fick's equation succeeded in predicting, on laboratory samples, this behaviour. In fact, The non-linear behaviour was shown to correlate well with Pore Size Distribution (PSD) of laboratory tested samples whose PSD distribution was measured experimentally using a mercury injection capillary pressure test method. The model predicts also the non-linearity of the electrical resistivity for sufficiently high current densities. In this paper, we show that non-linear behaviour of resistivity and chargeability vs. supplied current density can be met in field measurements, provided they are carefully planned. In a site located in Northern Apennines, where a saturated sandstone outcrops, different values of resistivity and chargeability were obtained at different supplied electric current whose achieved results agree with the forward model. Moreover, the non-linearity can also perturb TEM data as being affected by this IP effect, as the model predicts a dependence of non-linearity also on the current supply length. An example of anomalous TEM data collected in Northern Apennines is also presented and discussed.
Observed linear and non-linear IP effects - A summary of joint Italy-South Africa bilateral projects 2007-2014
Bignardi S.;
2015-01-01
Abstract
Among the several types of induced polarization effects, electro-osmosis and membrane polarization by constrictivity of pores my result in non-linear behaviour, i.e. chargeability is not constant with supplied dc current. A new model, based on the second Fick's equation succeeded in predicting, on laboratory samples, this behaviour. In fact, The non-linear behaviour was shown to correlate well with Pore Size Distribution (PSD) of laboratory tested samples whose PSD distribution was measured experimentally using a mercury injection capillary pressure test method. The model predicts also the non-linearity of the electrical resistivity for sufficiently high current densities. In this paper, we show that non-linear behaviour of resistivity and chargeability vs. supplied current density can be met in field measurements, provided they are carefully planned. In a site located in Northern Apennines, where a saturated sandstone outcrops, different values of resistivity and chargeability were obtained at different supplied electric current whose achieved results agree with the forward model. Moreover, the non-linearity can also perturb TEM data as being affected by this IP effect, as the model predicts a dependence of non-linearity also on the current supply length. An example of anomalous TEM data collected in Northern Apennines is also presented and discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
