Characterizing pore fabric in sandstones with magnetic anisotropy methods: initial results

Abstract

We describe and test a method to determine the directional properties of pore fabric in siliciclastic rocks using magnetic techniques. The approach is based on injecting into rock specimens a ferrofluid, a stable colloidal suspension of sub-domain magnetic particles in a liquid carrier, and measuring the magnetic susceptibility in different directions. Because the magnetic susceptibility after impregnation increases thirty times, the rock susceptibility can be neglected and therefore the anisotropy of magnetic ferrofluid susceptibility (AMFFS) provides an image of the 3D fabric and porosity in the rock. Our results on Triassic red sandstones suggest that both interparticle and intraparticle pores, which are measurable via AMFFS, are present and are largely determined by the micas and clays. Interparticle pores are most likely found between clay platelets, whereas intraparticle pores correspond to cleavage-plane pores within clay aggregates. Overall this study highlights that magnetic methods can be readily applied to siliciclastic rocks to characterize pore networks and more important, to determine the preferred orientation of the pores assemblage.