Compaction Bands in Porous Rock

Compaction bands are localized, planar zones of compressed material that form perpendicular to the maximum compressive stress. Compaction bands have been observed in porous sandstone formations in the field and in laboratory compression tests on porous sandstone, plaster, glass beads, polycarbonate honeycombs and metal foams. Because the permeability of the compacted material is much reduced, compaction bands can form barriers to fluid flow and adversely affect attempts to inject or withdraw fluids from porous reservoirs. An analysis of conditions for the onset of compaction bands as a bifurcation from homogeneous deformation indicates that they can occur when the stress strain curve for uniaxial compressive deformation has a peak. Formation of compaction bands is favored by significant compactive inelastic deformation and by a reduction in the yield stress for shear with increasing compressive mean stress. These conditions are typical for stress states on a “cap” yield surface often used to model the inelastic deformation of porous geomaterials.