Open AccessMagnetic pore fabric analysis: a rapid method for estimating permeability anisotropy
Author(s) -
Pfleiderer S.,
Halls H. C.
Publication year - 1994
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1994.tb02125.x
Subject(s) - anisotropy , permeability (electromagnetism) , isotropy , geology , petrophysics , materials science , porosity , permeameter , pore water pressure , composite material , magnetic anisotropy , porous medium , mineralogy , geotechnical engineering , hydraulic conductivity , magnetic field , magnetization , optics , soil science , chemistry , soil water , biochemistry , physics , membrane , quantum mechanics
SUMMARY The average orientation and fabric anisotropy of interconnected pore spaces in sandstones is derived from magnetic pore fabric analysis, a new technique which measures the anisotropy of magnetic susceptibility (AMS) of samples impregnated with a magnetic suspension. In magnetic pore fabric analysis, the permeable part of the porous network, consisting of pore bodies connected by pore throats, is rendered magnetically susceptible. AMS directly yields the average elongation direction of pore bodies and offers a simple way to investigate the effect of pore‐shape anisotropy on petrophysical parameters such as hydraulic and electrical conductivity. AMS‐derived pore fabric of sandstones of moderate diagenetic state is compared to permeability anisotropy measured directly on the same specimens. For any one sample, the orientation of the two tensors and their representation ellipsoids correlate closely. The preferred orientation of interconnected pores facilitates fluid flow parallel to the direction of pore elongation and causes the observed anisotropy of permeability. Axial ratios of the two anisotropy ellipsoids correlate less closely but show a trend of proportionality. Compared to the time‐consuming measurement of directional permeabilities, magnetic pore fabric analysis may, therefore, provide a rapid way to estimate the orientation and, to a lesser extent, the degree of permeability anisotropy in porous sandstones. The analysis of six specimens extracted from a large, homogeneous block sample proves the accuracy and reliability of the method. In five fluvial sandstone samples, maximum permeability and pore elongation are roughly parallel to the palaeocurrent direction. Therefore, magnetic pore fabric analysis can also be used to study the relationship between permeability, pore fabric and sedimentary structures.