Mechanisms of rock breaking by swirling-round SC-CO<sub>2</sub> jet

Abstract

Supercritical carbon dioxide (SC-CO2) jet is characterized by low rock breaking threshold pressure and high rock breaking rate. Swirling-round jet, taking the advantages of both swirling and round jet, enjoys high rock breaking efficiency. By integrating swirling-round jet and SC-CO2, it is prospective for swirling-round SC-CO2 jet to improve rock erosion efficiency further. Rock damage mechanisms of swirling-round SC-CO2 jet are investigated by means of rock-erosion experiments and scanning electron microscope (SEM) observation. The selected core samples include shale, dolomite as well as sandstone. For shale, no macro-deformation occurs and microscopic damage is discovered, forming tiny cracks. For dominate and sandstone, erosion holes form, and crystal particle cleavage as well as inter-particle rupture occur. According to the observation results, the rock damage mechanisms of swirling-round SC-CO2 jet are divided into two aspects. On the one hand, swirling-round SC-CO2 jet breaks rock by combining axial impinging, radical tension and circumferential shear. On the other hand, with characteristics of low viscosity, compressibility and strong diffusivity, numerous micro fractures are caused by SC-CO2, and existing fractures are expanded, which led to fractures joining together and massive rocks split off.