Study on failure mechanism of tight sandstone based on moment tensor inversion

Abstract

Understanding deep rocks' mechanical properties and failure evolution is crucial for efficient resource development. This study investigates the mechanical properties of tight sandstone and analyzes its acoustic emission (AE) characteristics using a combined discrete element model and moment tensor inversion. The AE activity during loading is categorized into three stages: crack initiation, stable crack propagation, and unstable crack propagation. Confining pressure loading suppresses AE activity during the crack initiation stage due to damage healing phenomenon. Moment tensor inversion reveals that tensile failure is the primary AE failure source, despite samples exhibiting splitting and shear failure modes. The proportion of AE failure types varies with stress levels and depends on the mechanical environment. Microcracks initiate at the ends of the sample and propagate inward along the loading direction, resulting in a blank area of AE events in the middle. This blank area can be utilized to predict specimen failure mode. The b value, representing the ratio of small to large magnitude events, decreases with increase of the confining pressure, indicating higher energy release during specimen failure under high confining pressure. The research results can provide a reference for predicting the failure of tight sandstone.