Influences of Supercritical Carbon Dioxide Jets on Damage Mechanisms of Rock

The supercritical carbon dioxide (SC-CO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {CO}_{2}$$\end{document}) jet is potentially a new type of rock-breaking method that effectively combines pressure impact and thermal shock. Current studies show that carbon dioxide jets produce a larger damaged area and require a lower threshold pressure of breaking rocks compared with that of water jets; however, the generation mechanism of these types of jets has not been clearly explained. This study developed a fluid–solid heat coupling model using ANSYS. The simulation and experimental results show a good agreement, clearly explaining the relationships between the damage shape and thermal stress. The results of the experiment conducted indoors at ambient temperatures were first explained by simulating the stress of the rock. When the thermal effect was considered, both the maximum stress and the area wherein the stress was high increased. The increase in the elastic modulus, Poisson’s ratio, and thermal expansion of the rock transformed its damage shape from bowl to linear. The increase in the injection pressure difference increased the broken depth of the rock, while the damage area on the surface of the rock remained the same. The possible damage shapes of the rock at formation temperature were analyzed. The temperature field of the jet increased both the shear stress acting on the surface of the rock and the tensile and shear stresses inside the rock; hence, the rock developed deeper and broader volumes of breaking in the well drilling process.