Three-phase flow analysis of rising shallow methane hydrate in gas lift system

Three-phase flows of rising shallow methane hydrate (MH) in a gas-lift system are numerically studied. One-dimensional simulations of the motion driven by compressed gas injection into a vertical pipe are performed using a Simplified Marker-and-Cell (SMAC) method, in which the gas compressibility and the phase change are considered. To clarify the optimal operation and design conditions, we investigate the relationship between the MH volumetric flow rate Qs and the injection gas one Qg,inj with varying the pipe diameter D and the depth of gas injection Lg,inj. For each D, the range of Qg,inj, in which the system can operate is determined from the relationship, and a unified relationship that can be arranged by the Froude number is obtained through the normalization under the conditions that the MH decomposition seldom occurs. For smaller MH particles, the amount of gas generation owing to the phase change is greater, promoting the self-gas-lift effect, and the scaling relationship is violated. The impact of the self-gas-lift effect also varies significantly considering different heat transfer coefficients between MH and surrounding water, and further elaboration and refinement are necessary for the heat transfer model.