Comparative Study on Mineral-Scale Microcrack Propagation of Shale under Different Loading Methods

Producing a sufficient volume of multiscale crack networks is key to enhancing recovery of shale gas. The formation of crack network largely depends on initiation and propagation of microcracks. To reveal the influence of different loading methods on the propagation of mineral-scale microcracks, this study used the Voronoi tessellation technique to establish a cohesive zone model of shale mineral distribution and applied six different boundary conditions to represent different loading methods. Crack path characteristics, rupture characteristics, continuous crack propagation and turning, and en echelon intermittent crack propagation under different loading methods were compared and analyzed. The essence of different loading methods affecting the length and complexity of cracks was the spreading range of tensile microcracks. The mechanical properties of minerals led to dissimilarities in continuous crack propagation and turning. The formation and propagation of en echelon intermittent fractures of different scales were mainly impacted by the heterogeneity of minerals and mineral aggregates. The spreading direction and connection form of en echelon intermittent fractures were mainly affected by the loading method. Conclusions arising from mineral-scale simulations contribute to understanding the mechanism of microcrack propagation resulting from different loading methods, and these conclusions have a guiding significance to enhanced shale gas recovery.