Dielectric behaviour of shale and calcareous sandstone of Jodhpur region

Abstract

Dielectric permittivity ɛ<i>'</i> and loss ɛ<i>"</i> of dry and water saturated shale, sandy sandstone (sandy shale) and calcareous sandstone of Jodhpur region were studied at room temperature in the frequency range from 100Hz to 100kHz and also at 10.1 GHz. It is observed that the ɛ<i>'</i> values of these samples decrease with increase in frequency. The complex plane plots(ɛ<i>"</i> &nbsp;versus ɛ<i>'</i>) of these geological materials are Cole-Cole arcs. The low frequency limiting dielectric constant ɛ_o, high frequency limiting dielectric constant ɛ, dielectric relaxation time τ and distribution parameter α of these samples have been determined from these Cole-Cole plots. The ac conductivity of dry and water-saturated samples has also been reported. The large enhancement in the permittivity value of water-saturated samples was found due to electrochemical polarization. Further it is observed that the increase in ɛ<i>'</i> value of water saturated shale and sandy sandstone is proportional to the volume fraction of water absorbed in the samples. The effect of the density, porosity, grain sizes and chemical composition on the frequency dependent dielectric permittivity of these samples has been explored.