Preliminary Experiments for Construction of an Evaluation Model for Methane Hydrate Transportation

Methane hydrate has been found below the seafloor in Japan’s Exclusive Economic Zone (EEZ) in a large amount. During the methane hydrate transportation, it is concerned that the riser pipe or the flowline can be plugged by the hydrate reformation and the freezing of seawater. The degradation and reformation kinetics of methane hydrate are mainly controlled by temperature, pressure, and methane concentration in the system, however, it is difficult to predict these factors in the multiphase flow because they are affected by fluid dynamics and heat transfer. Therefore, we are currently constructing an evaluation model for the slurry transportation, including the formation and dissociation processes of the hydrate in a riser pipe at dynamic conditions. Then, the characteristics of the phase change by the hydrate’s formation and dissociation have been investigated using experimental apparatus simulating the flow situations in a riser pipe. This paper reports some data obtained in two preliminary experiments on the heat transfer effect of pipes and the hydrate formation process. The formation processes of gas hydrate at a gas-liquid interface under high-pressure conditions were observed by using a probe-type video camera. The experimental results showed that the formation of gas hydrate requires enough amount of gas injection, including the dissolved gas in seawater, in addition to temperature-pressure condition.