Continuous Monitoring of the Elasticwave in the Methane Hydrate Generation and Dissociation in the Large-Scale Laboratory Reactor

We describe a monitoring of the elastic wave propagation in the methane hydrate-bearing sediment artificially formed in a giant pressure-cell. The giant pressure-cell consists of a cylindrical shaped cell with internal radius 50 cm and a vertical well system to simulate the depressurization method. The 6 cm thickness of iron wall of the cell shades the interior from the X-ray CT or the other electric non-destructive inspections. Therefore, the acoustic tomography survey with explosion-proofed piezoelectric sensor was proposed. As a first step, we conducted a preliminary minimal experiment by one source and three receivers to investigate the sufficiency of the system for the measurement. The sediment base was made of the Toyoura standard sand. In the final stage of the generation of methane hydrate, the P-wave velocity estimated from the travel time picked on the averaged waveform was about 3000 m/s which was consistent with previous research. In the dissociation stage, the rapid decay of the signal was observed after the initiation of the dissociation. The travel time delay was not observed before the signal disappeared.