Numerical Simulation Study on the Solid-Carrying Capacity of Hydrate–Sediment Slurry in a Vertical Pipe

Abstract

Solid fluidization is a green mining developed method for seabed nondiagenetic gas hydrate reservoirs, which can safely and controllably transport hydrate to land through seabed mining, closed fluidization, and gas–liquid–solid multiphase lift. However, there are many technical problems, such as hydrate and sediment fluidization and improvement of pipeline transportation capacity in the process of multiphase lift. Based on forced spiral flow in a vertical pipe, the numerical simulation of hydrate and sediment slurry in a vertical pipe with a twisted tape is carried out to explore the solid-carrying capacity of spiral flow and expand the safe boundary of multiphase flow. The effects of hydrate volume fraction, Reynolds number, hydrate particle size, and sediment particle size on turbulent kinetic energy, turbulent dissipation, solid volume fraction, and pressure of hydrate–sediment slurry have been studied. The results show that turbulent kinetic energy and turbulent dissipation decrease with the increase of hydrate volume fraction. The turbulent kinetic energy and turbulent dissipation increase with the increase of the Reynolds number. The concentration gradient of hydrate and sediment at the outlet section is larger than that of the horizontal spiral pipe. The hydrate particle volume fraction at the hydrate axis increases with the increase of hydrate volume fraction, Reynolds number, and hydrate particle size. Sediment particles are mainly distributed near the pipe wall, and hydrate particles are mainly distributed on the inner side of the sediment and form a high-concentration ring. The pressure change in the vertical pipe is similar to that in the horizontal pipe. When Re = 30,000, the critical volume fraction of hydrate blockage in the vertical pipe is 47%, while the critical volume fraction is 22% in the vertical smooth pipe. The transport capacity of hydrate particles is increased by 1.14 times. Under the same conditions, the pressure drop of the whole pipe exceeds that of the ordinary smooth pipe by about 15%.