Study on gas–water–solid three-phase flow characteristics and critical sand transport model in gas wells

Sand production in water-producing gas wells commonly occurs in sandstone gas reservoirs and during the initial production phase following fracturing operations. When sand particles in the wellbore cannot be normally transported out, this will affect the efficient development of natural gas. Critical sand transport velocity is a key parameter for determining whether sand particles in the wellbore can be transported to the surface, and its influencing factors and prediction methods urgently need in-depth research. To study the effects of different factor conditions on sand transport patterns and establish a gas–liquid–solid three-phase sand transport prediction model, providing theoretical support for sand control in gas wells. A large-scale multiphase pipe flow physical simulation experimental apparatus was employed to conduct three-phase flow sand transport characteristic experiments under ambient temperature and pressure conditions. The study systematically investigated the effects of gas flow rate (1–120 m3/h), liquid flow rate (0.1–3 m3/h), well inclination angle (0°–90°), and sand particle diameter (125–300 μm) on sand transport patterns. Experimental results indicate that liquid flow rate is the primary factor affecting critical sand transport, with critical sand transport gas velocity decreasing as liquid velocity increases. The effect of well inclination angle on sand transport exhibits an arch-shaped trend of “first high then low,” with the greatest sand transport difficulty occurring in the 30°–60° well section. Critical sand transport gas velocity increases with increasing sand particle diameter. Through force analysis of individual sand particles, considering the comprehensive effects of gas-phase drag force, liquid-phase drag force, buoyancy force, gravity, friction force, and shear force, a new gas–water–sand three-phase critical sand transport model was established. The model introduces angle correction coefficients and particle diameter correction terms. Validation was performed using 162.