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, subparallel, 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.