Abstract The supercritical carbon dioxide (SC-CO 2 ) jet has great potential for application in oil and gas drilling and exploitation engineering as its low threshold pressure and high efficiency. However, currently, the high energy consumption of SC-CO 2 jet rock breaking limits its application. It is an effective way to reduce energy consumption and further improve rock breaking efficiency by taking advantage of SC-CO 2 jet’s high impact stress, dissolution and thermal cracking. To clarify the thermal cracking effect of SC-CO 2 jet on coal and rock mass, the phase transition temperature and its effect on ambient temperature during SC-CO 2 jet injection were investigated experimentally in this paper. Under the premise of isolating impact stress, dissolution and extraction, experiments were conducted to examine the coal cracks induced by thermal stress. Additionally, experiments were conducted to induce coal crack using low-temperature nitrogen. Scanning electron microscopy and industrial CT scanning were used to analyze the surface and internal cracks of the samples. The results show that the environment temperature is decreased while the temperature of SC-CO 2 jet is decreased. And when the initial temperature of the jet is increased, the environment temperature will be further reduced. In addition, the thermal stress applied to coal at low temperature can promote the development and expansion of cracks on the coal surface and inside. In contrast, the thermal stress produced by low temperature nitrogen can only affect the surface cracks of coal. Furthermore, increasing the initial temperature of the jet can improve the development and expansion of the crack.
Wei et al. (Sat,) studied this question.