Compaction
Localization—Rule or Exception During Sandstone
Burial?
Eichhubl, Peter1 (1) The University of Texas at Austin, Austin, TX
The localization of compaction into
narrow zones has been documented in the field and reproduced in the laboratory.
In the field, compaction localization is expressed as sets of tabular
compaction bands. Their effect on the permeability structure, resulting in a horizontal permeability anisotropy of up to two orders of
magnitude, has been documented through field observations and numerical models.
Unclear is the significance of compaction localization for porosity reduction
during burial compaction of sandstone reservoirs. Scanline
surveys and porosity measurements of compaction bands in the Jurassic eolian Aztec Sandstone at Valley of Fire, NV, indicate that closely
spaced compaction bands locally account for as much as 27% of bulk volume,
resulting in up to 38% reduction in rock porosity. Compaction bands occur in
two roughly orthogonal sets of 10-100 cm spaced subvertical
bands, and a third set of bedding-parallel compactions bands. These widely
spaced compaction bands occur throughout the stratigraphic
section, though dominantly in the top third of the section. In addition, 0.5 to
1 cm spaced compaction bands, referred to as compaction lamellae, occur in
addition, and parallel, to the widely spaced compaction bands. The occurrence
of compaction lamellae appears confined to the vicinity of the Sevier Willow
Tank thrust, and is attributed to deformation ahead of the advancing thrust
sheet. Based on these current results it is suggested that compaction
localization is the dominant mode of porosity reduction under specific stress
loading conditions typically associated with tectonic processes.