Monitoring method of phase transition interface for natural gas hydrate based on thermoacoustic effect

In the drilling and exploitation for natural gas hydrate, the decomposition of combustible ices creates the interface between their solid state and liquid state, which would play an important role in the dynamic monitoring while exploitation. In this paper, a monitoring method based on the thermoacoustic effect is proposed to detect the position of the interface. The mechanism of the thermoacoustic coupling is introduced into the natural gas hydrate, that is, the physical model of thermoacoustic effect is established and detailed when the hydrate is excited by a strong electrical pulse. Two kinds of acoustic sources, the thermoelastic source and the phase transition acoustic source, are proposed to explain the obviously enhanced acoustic signals. By modeling and simulating, it is verified that the acoustic signals can be generated by the phase transition around the interface in hydrate. At the same time, many influencing factors on the thermoacoustic signals are researched based on simulations, such as the size of hydrate, the latent heat absorption coefficient and the amplitude of the transient electrical pulse. Finally, the experimental system both for hydrate generation and for thermoacoustic monitoring is built. We prepared carbon dioxide hydrate in a high-pressure reactor at an initial pressure of 5 MPa and temperature of −5 °C. Then take the hydrate into the environment of room temperature and standard pressure, apply the transient electrical pulse to the hydrate and use the ultrasonic probe to detect the acoustic signals. The results show that acoustic signals emitted from the position of the solid-liquid interface can be employed to monitor the hydrate decomposition experimentally and actually.