Microstructural Evolution of Porosity and Stress During the Formation of Brittle Shear Fractures: A Discrete Element Model Study
Morgan, Julia K.
Brittle fracturing in rocks is a progressive process involving changes in stress, strain, and porosity. Changes in these properties occur heterogeneously within a rock and are manifest at the grain scale, which is difficult to observe directly in the laboratory or the field. This study uses the discrete element method to show that fractures correspond to zones of generally lower stresses, higher porosity, and highly localized dilation and distortional strain. Using the discrete element method, we conducted numerical biaxial experiments at different confining pressures to probe the internal conditions of a low cohesive sandy sediment numerical analog. When compression begins, the stresses within the sandy sediment are relatively homogeneous with anastomosing stress chains. At yield stress, when the confining pressure is relatively low, multiple dilational bands start to open. At peak stress, high‐magnitude stress chains localize adjacent to the developing shear band and distortion is evident. Postpeak stress, through‐going shear fractures are fully developed. High stresses are transmitted across the fracture where porosity is low through a network of particles in contact. With increasing confining pressure, distortion is favored over dilation during deformation. Also, the number of particles that define the width of a stress chain across a shear fracture, and the steepness of the fracture, increases. Our results can be applied to understanding stress conditions of field samples, and in constraining rock property changes during reservoir modeling of fractured reservoirs.