The compound bridge plug staged fracturing technology in horizontal wells is widely used in the development of unconventional oil and gas fields. After fracturing, the bridge plug in the well needs to be milled out. The metal particles in the bridge plug milling debris have high density and large size, which requires appropriate flow rate to be carried out of the wellbore. According to the theory of liquid-solid two-phase flow and considering the physical characteristics of metal particles in bridge plug milling debris, the calculation model of minimum flow velocity required to carry metal debris in highly deviated well section was established, and the metal debris migration experiments in highly deviated well section were carried out. The experimental results are in good agreement with the calculated results of the theoretical model. It is found that the minimum velocity required for particle migration increases with the increase of particle diameter and density and the decrease of well inclination. The particle distribution has a great influence on the fluid drag force on the particles. When the particles gather together, the average drag force on the particles will decrease, which means the particles are difficult to migrate.
