On the pore-scale mechanisms leading to brittle and ductile deformation behavior of crystalline rocks

Abstract

SUMMARYDeformation mechanisms at the pore scale are responsible for producing large strains in porous rocks. They include cataclastic flow, dislocation creep, dynamic recrystallization, diffusive mass transfer, and grain boundary sliding, among others. In this paper, we focus on two dominant pore-scale mechanisms resulting from purely mechanical, isothermal loading: crystal plasticity and microfracturing. We examine the contributions of each mechanism to the overall behavior at a scale larger than the grains but smaller than the specimen, which is commonly referred to as the mesoscale. Crystal plasticity is assumed to occur as dislocations along the many crystallographic slip planes, whereas microfracturing entails slip and frictional sliding on microcracks. It is observed that under combined shear and tensile loading, microfracturing generates a softer response compared with crystal plasticity alone, which is attributed to slip weakening where the shear stress drops to a residual level determined by the frictional strength. For compressive loading, however, microfracturing produces a stiffer response than crystal plasticity because of the presence of frictional resistance on the slip surface. Behaviors under tensile, compressive, and shear loading invariably show that porosity plays a critical role in the initiation of the deformation mechanisms. Both crystal plasticity and microfracturing are observed to initiate at the peripheries of the pores, consistent with results of experimental studies.

Responses of chemically active and naturally fractured shale under time‐dependent mechanical loading and ionic solution exposure

“…Such fracture property differences are not studied in this paper. For the case of open and closed fractures, numerical methods can be found in previous studies …”

On the risk of hydraulic fracturing in CO2geological storage

“…Interaction at the pore-scale between crystal plasticity and fracturing which can explain the mechanism of fracture toughness was studied in [21]. [9].…”

Numerical analysis of the effect of natural microcracks on the supercritical CO2 fracturing crack network of shale rock based on bonded particle models

“…Although the continuum‐type method has no model size problem, it is not very good at simulating microscopic mechanisms (such as the evolution of microcracks). The computational framework presented by Tjioe and Borja can accommodate the presence of pores in the solid and the stress concentrations that develop in the edges and corners of the pores and capture the microfracture processes . Pore‐scale modeling approaches are indeed very good methods that can address not only large‐scale engineering but also micromechanisms.…”