Numerical Simulation of Capacitively Coupled Resistivity Imaging Measurements on Rock Samples

Estimation of electrical properties in permafrost studies can benefit from capacitive resistivity imaging (CRI), which overcomes the limitations of usual electrical resistivity imaging employing galvanic coupled electrodes. However, the response of these systems is not fully understood yet. We have used numerical finite element modelling to investigate the complex transfer impedance as measured by a quadrupole consisting of sensors with finite dimensions. Next to a parameter study over a homogeneous halfspace, also an actual experimental setup is modelled. The numerical results are compared to a quasi-static approximation based on point-poles and measured data, respectively. The parameter study shows that the real part of the complex transfer impedance can be approximated by the quasi-static approach in case the dipole separation is large compared to the sensor dimensions. It is shown that quantification of the imaginary part is difficult and depends strongly on the geometric setup. The results of the simulation of a 3D finite rock sample indicate that finite element modelling can be a practical tool for improving the understanding of the experimental data and for performing a better error analysis.