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to 2 m, with both sets in a cross-hatch pattern typically exhibiting similar spacing. The
cross-hatch pattern is both less abundant and less persistent than the parallel and
anastomosing DB patterns, and often at least one DB set within a cross-hatch pattern
terminates at the nearest dune boundary. The two sets of DBs within the cross-hatch
patterns exhibit mean orientations generally similar to those of any two of the three
dominant orientations described above for the parallel pattern case, and commonly
intersect with an acute angle of ~80°.
4.3. Anastomosing
Anastomosing patterns of DBs consist of sub-parallel, intersecting bands generally
exhibiting the same dominant, high-angle-to-bedding orientation described above for the
parallel pattern, but with trends and dips varying by 25 degrees or more over the scale of
centimeters to meters (Figure 6.5). Deformation bands within the anastomosing patterns
exhibit ranges of thickness (up to ~1.5 cm) and spacing (centimeters to meters) similar to
those reported above for the parallel case. Anastomosing band sets have previously been
described in the literature, but always as existing in narrow zones of very closely spaced
bands—typically associated with faults having distinct slip planes (Aydin, 1978; Aydin
and Johnson, 1983). In the Aztec, however, anastomosing DB arrays commonly cover
areas up to hundreds of meters on a side, while passing through multiple dune
boundaries. Indeed, the anastomosing pattern of steeply dipping, generally north-trending
DBs dominates the Aztec, and the arrays of approximately parallel DBs described above
can reasonably be considered as simply more orderly sub zones within the greater,
anastomosing configuration.
5. Numerical modeling methods
Numerical techniques can be used to calculate effective permeability for any
characteristic DB pattern that can be represented as a finely meshed grid of cells, each
cell specifying either DB or sandstone matrix permeability (Figure 6.6). The method
involves solving a single fluid phase, steady state pressure equation subject to spatially
periodic boundary conditions over the entire grid to yield this upscaled or effective
permeability. The fluid flux and pressure boundary conditions are said to be spatially
periodic insofar as they implicitly assume that the domain block in question is surrounded
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