Structural Study of Flow Tube Internal Highly Under-Expanded Well Blowouts

In the event of a well blowout, the flow tube is a commonly used device for controlling the flow. This solution has been demonstrated to be effective in the majority of cases. However, as drilling depths increase and spray pressure ratios grow, the gas flow from a well blowout transitions from a low-volume subsonic jet to a high-volume, under-expanded jet. This consequently results in an inability to install the flow tube. To enhance our understanding of the behavior of highly under-expanded jets in conventional flow tubes, this study uses FLUENT to perform three-dimensional simulations of the coupled flow field between such a jet and a flow tube (with a spray pressure ratio of 5.1 and a Mach number of 3.6). The present study begins with an analysis of the shock structure of the jet in proximity to the wellhead, thereby revealing the formation process of the Mach disk. It then investigates how varying the distance of the flow tube from the wellhead and its inlet and outlet diameters impacts the Mach disk structure. Subsequent analysis of the vortex structure and pressure conversion within the flow tube enabled us to elucidate the reasons for its unsuitability at well blowout accident sites. This study provides a theoretical justification for the failure of the flow tube to engage, through a structural analysis of the highly under-expanded blowout jet within the flow tube. This provides essential support for operations aimed at mitigating the consequences of blowouts.