Abstract

There is a systematic relationship between anisotropy in the fabric of rocks and anisotropy in their dielectric properties, although the relationship is difficult to express in any quantitative sense. In general, the dielectric constant K′, the dielectric loss K″, and the real conductivity σ′ are a maximum when measured along the lineation axis (L) of rock, and a minimum when measured along the foliation normal (F). In this study, rocks were measured both vacuum dried and with varying degrees of water present; the anisotropy of wet rocks is greater than when vacuum dried, due presumably to anisotropic distribution of water parallel to the petrofabric. The effects of water, however, can be eliminated by means of measurements in vacuum or, more simply, by heat drying the sample, and subsequent impregnation of the rock with a hydrophobic low-loss dielectric material (paraffin wax). This is particularly significant since it greatly reduces the cost and time involved in this type of study.Dielectric anisotropy is frequency dependent. It was largest at the lowest measurement frequencies (30 Hz) and diminished with increasing frequency. For this and other reasons, dielectric anisotropy in rock is attributed to Maxwell–Wagner effects, which are low frequency relaxation phenomena related to the shape, size, and dielectric anisotropy in rock, reflecting primarily the grain-shape and grain-aggregate-shape fabric.

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