structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
structural geology, propagation mechanics and - Stanford School of ...
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1. Abstract<br />
Chapter 7<br />
Flow <strong>and</strong> transport effects <strong>of</strong> compaction b<strong>and</strong>s in s<strong>and</strong>stone<br />
at scales relevant to aquifer <strong>and</strong> reservoir management<br />
Thin, tabular, low-porosity, low-permeability compaction b<strong>and</strong>s form pervasive, sub-<br />
parallel, anastomosing arrays that extend over square kilometers <strong>of</strong> exposure in the Aztec<br />
s<strong>and</strong>stone <strong>of</strong> southeastern Nevada—an exhumed analog for active aquifers <strong>and</strong> reservoirs.<br />
In order to examine the potential flow <strong>and</strong> transport effects <strong>of</strong> these b<strong>and</strong> arrays at scales<br />
relevant to production <strong>and</strong> management, we performed a suite <strong>of</strong> simulations using an<br />
innovative discrete-feature modeling technique to capture the exact pattern <strong>of</strong> compaction<br />
b<strong>and</strong>s mapped over some 150,000 m 2 <strong>of</strong> contiguous outcrop. Significant impacts related<br />
to the presence <strong>of</strong> the b<strong>and</strong>s <strong>and</strong> their dominant trend are apparent: the average pressure<br />
drop required to drive flow between wells exceeds that for b<strong>and</strong>-free s<strong>and</strong>stone by a<br />
factor <strong>of</strong> three, <strong>and</strong> is 10% to 50% higher across the b<strong>and</strong>s versus along them; reservoir<br />
production efficiency varies up to 56% for a typical five-spot well array, depending on its<br />
orientation relative to the dominant b<strong>and</strong> trend; <strong>and</strong> contaminant transport away from a<br />
point source within an aquifer tends to channel along the b<strong>and</strong>s, regardless <strong>of</strong> the regional<br />
gradient direction. We conclude that accounting for the flow effects <strong>of</strong> similar<br />
compaction-b<strong>and</strong> arrays would prove essential for optimal management <strong>of</strong> those<br />
s<strong>and</strong>stone aquifers <strong>and</strong> reservoirs in which they occur.<br />
2. Introduction<br />
The potential for deformation b<strong>and</strong> arrays at the outcrop scale to reduce bulk effective<br />
2-D permeability by more than an order <strong>of</strong> magnitude, <strong>and</strong> to induce significant (10x)<br />
permeability anisotropy, has been established (Sternl<strong>of</strong> et al., 2004). Their potential to<br />
cause asymmetric patterns <strong>of</strong> well drawdown has also been demonstrated (Matthai et al.,<br />
1998). However, despite growing recognition that deformation b<strong>and</strong> fabrics are common<br />
in both exhumed (e.g. Underhill <strong>and</strong> Woodcock, 1987; Edwards et al., 1993; Davis, 1998;<br />
Swierczewska <strong>and</strong> Tokarski, 1998; Cashman <strong>and</strong> Cashman, 2000; Shipton <strong>and</strong> Cowie,<br />
2001; Davatzes et al., 2005) <strong>and</strong> subsurface (e.g. Fossen <strong>and</strong> Hesthammer, 1998;<br />
Hesthammer et al., 2000; Hesthammer <strong>and</strong> Henden, 2000) s<strong>and</strong>stones, their ability to<br />
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