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

Finally, there is the issue of forecasting where volumetrically extensive compaction
and deformation band arrays are most likely to occur. This is an active area of research
that to date has emphasized discrete deformation band style faults in sandstone (e.g.
Aydin and Johnson, 1983, Shipton and Cowie, 2001; Davatzes et al., 2005) over the
distributed style of tectonic fabric formed by CBs in the Aztec (Sternlof et al., 2005).
Much of the research into both types of bands has focused on their occurrence in
Mesozoic æolian sandstones of the southwestern U.S., although deformation bands are
increasingly being identified in a wide variety of porous, granular geologic materials
ranging from nonwelded ignimbrites (Wilson et al., 2003) to unlithified Holocence beach
sands (Cashman and Cashman, 2000). Compaction bands, however, have yet to be
positively identified outside of the Navajo (Mollema and Antonellini, 1996) and Aztec
(Sternlof et al., 2005) sandstones. As of this writing therefore, the most that can be said is
that CB arrays such as exposed in the Aztec might reasonably be suspected in any high-
porosity sandstone that has been subjected to a differential tectonic stress prior to
substantial lithification.
7. Conclusions
In this study, we performed flow modeling using a state-of-the-art discrete-feature,
finite-volume simulator applied to a CB data set of unprecedented detail and scale, which
was derived from a real geological system that serves as an exhumed analog for active
sandstone aquifers and reservoirs. Our results demonstrate the potential for CB arrays,
such as abundantly exposed in the Aztec sandstone at the Valley of Fire, Nevada, to exert
profound effects on subsurface flow at scales relevant to aquifer and reservoir modeling
and production. Specifically, we found that:
• The CBs as mapped cause an average three-fold increase in the pressure drop
required to maintain a given flow rate between two wells, as compared to CB-free
sandstone;
• There is a mild directional aspect to this pressure effect—an anisotropy—with ∆P
across the dominant band trend exceeding that along the trend by an average of
25%; and
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