MEASURING TECHNIQUES FOR ROCKS WITH HIGH PERMITTIVITY AND HIGH LOSS

Abstract

In this paper, perhaps for the first time, more realistic trends for the electrical characteristics of rocks with high loss and high permittivity are demonstrated. With decrease in frequency, below [Formula: see text] hz, the dissipation factor of these rocks generally increases, while the real relative permittivity generally levels off at about l0 to 30. These results were obtained by use of the airgap and several correction techniques at the electrode‐specimen contacts. The rocks used in these measurements contain a certain amount of moisture since they were dried in room atmosphere. When these rock samples are measured by the conventional electrode contact method, the real relative permittivity rises with decrease in frequency, while the dissipation factor levels off at a value of about 1.0 or below. These results are contrary to those obtained by measurements with the airgap technique and by applying several correction factors. For a serpentinite specimen, real relative permittivity measured by the conventional contact method rises 10 times above that measured by the airgap technique. Most results published in the past on electrical characteristics of rocks containing moisture show trends similar to those made by the electrode contact method. Therefore, these results published in the past perhaps contain errors due to insufficient consideration of the electrode‐specimen contacts. Since the rocks used in this study are not saturated with moisture, no conclusion can yet be drawn. However, the results in this paper indicate some important considerations which should be taken into account in the measurements on moist rocks that exhibit high permittivity and loss characteristics.