Ip Interpretation In Environmental Investigations

IP measurements are sensitive to the low-frequency capacitive properties of rocks and soils,<br>which are controlled by diffusion polarization mechanisms operating at the grain-fluid interface.<br>Standard IP interpretation utilizes the conventional field IP parameters: chargeability, percentage<br>frequency effect and phase angle. These parameters are dependent upon both surface polarization<br>mechanisms and volumetric conduction mechanisms. Consequently, they afford a poor<br>quantification of surface polarization processes of interest to the field geophysicist. A parameter<br>that better quantifies the magnitude of surface polarization is the normalized chargeability,<br>defined here as the chargeability divided by the resistivity magnitude. This parameter is<br>proportional to the quadrature conductivity measured in the complex resistivity method.<br>Laboratory and field experiments were performed to determine the dependence of the standard<br>IP parameters and the normalized chargeability on two important environmental parameters:<br>salinity and clay content. The laboratory experiments illustrate that the chargeability is strongly<br>correlated with the sample resistivity, which is primarily a function of the bulk rock properties<br>(i.e., salinity, porosity, and saturation). The normalized chargeability is shown to be independent<br>of the sample resistivity and it is proportional to the quadrature conductivity, which is directly<br>related to the surface polarization processes.