LAUSR

Abstract Supercritical carbon dioxide (SC-CO2) jets are of increasing interest in drilling and completion engineering due to their superiority over water jets. To understand the nature of SC-CO2 jets and improve performance, the flow characteristics of SC-CO2 jets were experimentally investigated, followed by rock breaking tests. Flow images of the jet under various operating conditions were captured by a high speed CCD camera. A comparative analysis of an SC-CO2 jet flow with classical theories and other types of jet flows was performed. The results show that the submerged environment can greatly affect the characteristics of SC-CO2 jets. When injecting into a gaseous CO2 environment, the saturation curve is crossed and intense phase transition occurs in the jet flow. The jet appears as a classical single-phase gas/gas turbulent shear layer. Whereas, under an SC-CO2 submerged environment, shock waves can be found in the jet flow. The initial instability and spreading rate reduce with the increase in inlet pressure. The jet behaves as a typical compressible jet. These features are different from water jets and are most likely the reason for the better rock breaking performance of SC-CO2 jets. Further, SC-CO2 jets under a gaseous CO2 submerged environment are prone to result in large and shallow breaking pits, while the jets under an SC-CO2 environment tends to cause small and deep breaking pits.