Sand-Carrying Experiments with Supercritical CO₂ in a Horizontal Annulus

According to the similarity principle, a device for sand-carrying tests was developed to determine the sand-carrying performance of supercritical CO₂ in the horizontal annulus and analyze the effects of key operating parameters on the sand-carrying performance. The device was employed to explore the influence of the injection mass flow, sand concentration, outlet pressure, and fluid temperature of supercritical CO₂ on the sand migration in the horizontal annulus. The results showed that supercritical CO₂ could effectively carry sand in the horizontal annulus by means of suspension transport, and the increase in its mass flow could enhance the turbulence intensity of the fluid in the annulus and improve the sand-carrying effect by suspension transport. In a high sand concentration, sand beds were likely to occur at the bottom of the annulus, which reduced the open area and raised the sand transport velocity. Under the same injection condition, the sand transport velocity in the annulus decreased with the increase of outlet pressure, but the amplitude of reduction is gradually lowering. In addition, a rise in fluid temperature was conducive to the accumulation reduction of sand in the annulus in an appropriate temperature range. The research results can provide a reference for optimizing the key construction parameter design in drilling and fracturing with supercritical CO₂.