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

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