A Experimental Study on Bubble Migration Laws in Wellbore During Bullheading Killing

Bullheading killing is an effective well control method for dealing with early gas invasion in petroleum drilling. However, insufficient research on the migration law of gas bubbles under countercurrent and downflow conditions in the wellbore has led to an incomplete understanding of the gas phase bullheading mechanism and inaccurate design of well control parameters. To address these issues, this study conducted an analysis of gas-liquid two-phase flow under bullheading conditions using simulation experiments. The experiments were conducted using a transparent wellbore simulation device with an inner diameter of 0.1 m, equipped with precise measurement equipment such as high-speed cameras, gas-liquid flow meters, and pressure gauges. The study systematically investigated the effects of different well control fluid systems, physical parameters, and gas-liquid superficial velocities on the migration law of gas bubbles. The experimental results showed that under bullheading conditions, the gas bubble distribution coefficient C0 was significantly smaller than the commonly used value of 1.2 in existing models. Based on the experimental data, this study proposed an empirical formula for the gas bubble distribution coefficient suitable for this condition and established a calculation model for gas bubble migration velocity. The model demonstrated high accuracy in predicting gas bubble velocity. This study not only provides important theoretical and experimental support for the study of gas-liquid two-phase flow under similar bullheading conditions but also lays a solid foundation for optimizing the design of bullheading parameters.