Permeability Evolution during Deformation of Siliciclastic Sandstones from Moab, Utah

Abstract

We conducted triaxial deformation experiments on large (0.1-m; 0.33-ft)-diameter cores of four sandstones from the Moab area to investigate the effect of total axial strain and effective confining pressure on the evolution of bulk permeability of faulted samples. Sandstones with low bulk porosities (Dewey Bridge and Slickrock Subkha) exhibited an increase in permeability with increasing inelastic axial strain at low effective confining pressures, whereas those with high porosity (Navajo and Slickrock Aeolian) showed a decline in permeability. However, all samples showed permeability decline with increasing inelastic axial strain at high effective confining pressures. Meanwhile, microstructural observations revealed no systematic dependence of the width of the shear zone and the number of deformation bands on either strain or effective confining pressure, although grain-size reduction was more intense at high effective confining pressures. A new geometric model has been developed based on these observations for a constant effective confining pressure and is shown to provide excellent agreement with the experimental data at all effective confining pressures. However, the parameters of the model depend only weakly on effective confining pressure for low-porosity sandstones, suggesting that cataclastic fault seals in low-porosity rocks have a low sensitivity to burial depth in the range studied here.