| Summary: | Supercritical carbon dioxide (SC-CO<sub>2</sub>) jet is capable of decreasing the threshold pressure of rock breakage and mitigating formation damage, owing to its low viscosity, high diffusivity, and extremely-low surface tension. The swirling-round jet holds the advantages of both a swirling jet and a round jet. Therefore, the comprehensive technique, swirling-round SC-CO<sub>2</sub> (SR-SC-CO<sub>2</sub>) jet, is expected to substantially enhance rock-breaking efficiency. However, theoretical analysis of the flow field characteristics of SR-SC-CO<sub>2</sub> has not been reported yet. This work aims to lay a theoretical foundation for employing SR-SC-CO<sub>2</sub> in drilling and fracturing. The flow field is simulated using Naiver-Stokes equations and the RNG <i>k-ε</i> turbulence model. Sensitivity analysis, regarding pressure drop of the nozzle, confining pressure, fluid temperature, jetting distance, the diameter of the nozzle’s central hole, and grooving area, are performed. We show that the combined swirling-round SC-CO<sub>2</sub> jet flow could maintain a relatively larger axial as well as tangential velocity compared to a single approach of swirling jet or round jet, enabling one to acquire a deeper oillet and expand the perforation area effectively. The simulation results substantiate the enormous potential of SR-SC-CO<sub>2</sub> in improving rock-breaking efficiency and clarify the influence of relevant parameters on the impact pressure of the jet flow.
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