Model-based assessment of the effect of surface area growth on the permeability of granular rocks

This paper presents a methodology to track the evolution of hydraulic conductivity in granular rocks by accounting for the combined effect of porosity changes, grain breakage, and cement bond damage. The main objective was to use simplified continuum models to assess the relative role of different microscopic processes. For this purpose, the breakage mechanics theory was used and the computed deformation response was linked to the Kozeny equation, a permeability model able to evaluate the permeability loss resulting from the simultaneous decrease of the porosity and growth of the surface area. In particular, the evolution of the model's internal variables was linked to idealized geometric schemes at the particle scale, with the goal of distinguishing the contribution of the fines generated by the disaggregation of the cement matrix from that of the broken fragments resulting from the crushing of the skeleton. Compression-flow experiments available in the literature for different granular materials were used to test the performance of the proposed approach. The analyses illustrated that the drop in permeability would be severely underestimated without an accurate computation of the growth of the surface area.