Anomalous electrical resistivity anisotropy in clean reservoir sandstones

North, Laurence J. and Best, Angus I. (2014) Anomalous electrical resistivity anisotropy in clean reservoir sandstones. Geophysical Prospecting, 62 (6), 1315-1326. (doi:10.1111/1365-2478.12183).

Record type: Article

Abstract

We report novel laboratory measurements of the full electrical resistivity tensor in reservoir analogue quartzose sandstones with clay contents less than 1.5%. We show that clean, homogeneous, visually uniform sandstone samples typically display between 15% and 25% resistivity anisotropy with minimum resistivity normal to the bedding plane. Thin-section petrography, analysis of fabric anisotropy, and comparison to finite-element simulations of grain pack compaction show that the observed anisotropy symmetries and magnitudes can be explained by syn-depositional and post-depositional compaction processes. Our findings suggest that: electrical resistivity anisotropy is likely to be present in most clastic rocks as a consequence of ballistic deposition and compaction; compaction may be deduced from measurements of electrical anisotropy; and the anisotropy observed at larger scales in well logging and controlled-source electromagnetic data, with maximum resistivity normal to bedding, is most likely the result of meso-scale (10^-1 m – 10¹ m) periodic layering of electrically dissimilar lithologies.

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