Incipient motion behavior of the settled particles in supercritical CO2

Abstract

The incipient motion process of settled particles in supercritical CO2 was studied through experimental measurements and force analyses. By referring to the theories of sand-wind and sediment restarting, the incipient motion state description and mechanism were optimized to fill the theoretical gaps in particle restarting research in the petroleum industry. Visualization experiments were carried out under various temperature, pressure, and particle conditions. The critical pump rates for the onset of grain motion in supercritical CO2 were measured. A critical pump rate empirical formula was obtained based on the experimental results and a derived Shields number expression. The average critical Shields number in supercritical CO2 was 0.0028. The cohesive force on particles is zero in supercritical CO2 based on its non-interfacial-tension characteristic. The measured spinning rate of the restarting particles in supercritical CO2 was 121 r/s on average. Therefore, the calculated value of the Magnus force was approximately 30% of the force of gravity on particle. Particle incipient motion in supercritical CO2 has a varying driving force (Magnus force) and simple resistant force (lack of cohesive force), which enhances the incipient motion of particles in supercritical CO2.