Increased Fractured Rock Permeability After Percolation Despite Limited Crack Growth

Abstract

AbstractFractured rock permeability can increase by crack extension that creates additional flow pathways or by increases in crack openings that increase crack transmissivity. Understanding the partitioning between these two mechanisms during rock deformation is critical for conceptual models of fluid flow and transport in crystalline rocks and sedimentary layers with low matrix permeability and for the hydromechanics of crustal rocks. Using ice as a model for rock, new systematic experiments reveal that when subject to uniaxial loading at a constant strain rate, crack density remains nearly constant after the onset of percolation even while permeability increases, indicating that after the onset of percolation the increase in permeability is primarily due to the opening of existing cracks rather than the extension of cracks. These observations have implications for conceptual models of fractured rock permeability that often focus on the evolution of permeability with changing fracture density rather than changing fracture transmissivity and for attempts to link fractured rock permeability to seismic properties that often dominantly consider changes in crack density rather than crack apertures.