Microstructural Control of Nucleation and Development of Compaction Bands in Porous Sandstone

Abstract

Development of deformation bands in porous sandstone has primary importance on fluid flow in subsurface geologic reservoir and aquifer. Among diversity of compactant failure mode in porous rock, compaction bands are a type of deformation band characterized by reduction of porosity and permeability across the thin band structure. Previous laboratory studies show that discrete compaction band develop in several sandstones at stress states in the transitional regime between brittle faulting and cataclastic flow. To address fundamental question of what key parameter is in control of compaction band development, we compile existing data and present new systematic laboratory findings including mechanical data and microstructural observations on two porous sandstones, Bleurswiller and Boise, of similar porosity and mineralogy but different sorting. While discrete compaction bands developed in Bleurswiller that has a relatively uniform grain size distribution, bands were inhibited in poorly sorted Boise sandstone. Our results demonstrate that grain size distribution plays a fundamental role in compaction band formation. In the most homogeneous sandstones, tabular continuous bands can efficiently impact fluid flow whereas local heterogeneities make the bands more tortuous, less continuous, and in turn less efficient as permeability barrier.