Experimental and theoretical quantification of in-situ crushing characteristics of irregularly-shaped particles under multi-axis pressure with X-ray micro-computed tomography (μCT) and discrete element method (DEM)

In this study, an integrated and robust framework has been developed to experimentally and theoretically quantify the in-situ crushing characteristics of irregularly-shaped particles under reservoir conditions. Experimentally, a multi-axis pressure loading system was customized to evaluate the in-situ crushing behaviour of packed proppants utilizing the X-ray micro-computed tomography (μCT) analysis. Based on the reconstructed CT images, the particle crushing behaviour was evaluated and analyzed, and its key parameters (e.g., failure modes, particle size distribution (PSD), and mean coordination number (CN)) were quantitatively determined. Based on force chain and fracture propagation dynamics, theoretically, the discrete element method (DEM) has been employed to generate irregularly-shaped particles and thus confirm their morphologies of the reconstructed images so as to determine the simulation parameters. Particle failure modes are found to be influenced by both particle morphology and pressure loading conditions. Stress propagates along the force chains and then extends in chain-like or networked patterns. Along these paths, the principal stress directions of individual proppants vary, resulting in diverse failure modes. The crushing process transitions from a dynamic state to a steady one, during which sub-particles generated from crushed particles are compacted under the applied load and fill the entire pore spaces. Such compaction increases the overall average CN, while higher CNs are less likely to crush the larger particles in a given system. With lateral confining stress, the internal force chain network of the packed proppants is found to be more homogeneous, leading to the strain hardening effect and significant improvement of the compressive strength.