Research on Initiation of Carbon Dioxide Fracturing Pipe Using the Liquid Carbon Dioxide Phase-Transition Blasting Technology

Liquid carbon dioxide (L-CO 2 ) phase-transition blasting technology (LCPTB) has caused wide concern in many fields, but there is a lack of research on the initiation of the carbon dioxide fracturing pipe. Studies regarding the carbon dioxide fracturing pipe initiation are critical for controlling and optimizing the LCPTB. Therefore, in this article, a series of exploratory experiments of carbon dioxide blasting were carried out to investigate the qualitative and quantitative relationships between the carbon dioxide fracturing pipe initiation and the three key variables (the filling mass of liquid carbon dioxide (L-CO 2 ) ( X 1 ), the amount of chemical heating material ( X 2 ) and the thickness of the constant-stress shear plate ( X 3 )). The failure mechanisms of three variables on the phase-transition blasting process of a carbon dioxide fracturing pipe was analyzed qualitatively based on experiment temperature, strain curve and failure form of constant-stress shear plate. An empirical model between the carbon dioxide fracturing pipe initiation ( Y ) and the three key variables ( X 1 , X 2 , X 3 ) was obtained after processing experiment result data quantitatively. Based on the phase-transition and blasting process of carbon dioxide, two methods, the Viral–Han–Long (VHL) equation of gas state (EOS) and the strength-failure method were used to calculate the blasting pressure and determine the failure mode of the fracturing pipe. The proposed blasting empirical model can be used to optimize the structural design of carbon dioxide fracturing pipes, guide on-site carbon dioxide blasting operations and further achieve the best blasting effect of LCPTB, so this work can enable LCPTB to be better applied to practical projects.