Microstructural Controls on the Uniaxial Compressive Strength of Porous Rocks Through the Granular to Non-Granular Transition

Abstract

Under uniaxial compression, a porous rock fails by coalescence of stress-induced microcracks. The micromechanical models developed to analyze uniaxial compressive strength data consider a single mechanism for the initiation and propagation of microcracks and a fixed starting microstructure. Because the microstructure of clastic porous rock transitions from granular to non-granular as porosity decreases during diagenesis, their strength cannot be captured by a single model. Using synthetic samples with independently controlled porosity and initial grain radius we show that high-porosity granular samples, where microcracks grow at grain-to-grain contacts, are best described by a grain-based model. Low-porosity non-granular samples, where microcracks grow from pores, are best described by a pore-based model. The switch from one model to the other depends on porosity and grain radius. We propose a regime plot that indicates which micromechanical model may be more suitable to predict strength for a given porosity and grain radius.