structural geology, propagation mechanics and - Stanford School of ...

By contrast, band-parallel effective permeability is not reduced by an order of magnitude
until wb/W=90%, a DB volume density far exceeding the approximate upper limit of 20%
observed in the Aztec. Thus for parallel DB patterns within the realistic wb/W range, a
permeability anisotropy of up to 2 orders of magnitude can be expected, with the
maximum permeability oriented in the band-parallel direction (Figure 6.9). Note also that
band-parallel effective permeability for both kb/km=10 -2 and 10 -3 are virtually
indistinguishable below wb/W=80%.
6.2. Cross-hatch
Cross-hatch DB sets in the Valley of Fire exhibit a consistent acute intersection angle
of ~80°. In other locales, intersection angles ranging from ~20° to ~90° have been
reported (Aydin and Reches, 1982; Hill, 1989; Jamison and Stearns, 1982; Underhill and
Woodcock, 1987). We begin our analysis of the effective permeability of cross-hatch
patterns by studying those of evenly spaced, orthogonal DB sets as a function of kb/km
and wb/W. Figure 6.10 compares our numerical modeling results for kb/km=10 -2 to an
analytical approximation presented by Taylor and Pollard (2000) and band-normal
effective permeability as calculated by harmonic averaging. The numerical and harmonic
averaging results match well over the entire wb/W range, but correspond to the analytical
approximation only for wb/W below about 5%. For kb/km=10 -3 the wb/W range of
correspondence drops to