Numerical simulations of methane hydrate particles around the bottom of the recovery pipe of the gas-lift method

Methane hydrate has recently attracted attention as a potential energy resource, which might be recovered from the deep seabed by means of a gas lift recovery system. This study examined the flow of seawater and behavior of hydrate particles around the bottom of the riser pipe by simulation and experiment in order to determine the optimal shape of the bottom of the pipe and the optimal operating conditions. The finite differential method and the discrete element method were combined to simulate the governing equations of sea water as a continuum and hydrate particles as discrete elements. The simulation results agreed reasonably well with the experimental results conducted for the laboratory-scale riser pipe with height of 1.5 m and diameter of 0.05 m. The simulations for the actual scale with diameter of 1m showed that the optimal shape at the bottom of the rise pipe is umbrella-shaped with a 45° degree slope and height of 0.4-0.6 m. The simulations also showed that the gas-lift method is sufficiently effective and economical if the hydrate layer at the seabed can be crushed into small pieces with diameter of 0.1m.