To meet the needs of conducting natural gas hydrate simulation experiments, detecting electrical and acoustic parameters and establishing the relationship between the parameters and hydrate saturation, a joint electrical-acoustic detection apparatus was developed first, then a series of methane hydrate formation and decomposition simulation experiments was carried out with electrical and acoustic parameters detected, and finally the electrical and acoustic response characteristics were analyzed and discussed. It has been demonstrated that: (1) the electrical impedance spectra with a wide range of frequencies and ultrasonic signal waveforms can be obtained synchronously by utilizing the joint electrical-acoustic detection apparatus; (2) the space distribution information of electrical and acoustic parameters can be obtained through the designed electrical-acoustic compound sensors, array-arrangement scheme and the ‘time-sharing and rotating’ working mode of sensors; (3) the impedance modulus with a frequency of 100 kHz selected based on the proposed evaluation specifications, i.e. the fluctuation percentage and correlation coefficient, decreases first and then increases with an increasing hydrate saturation, and the fluctuation amplitude of the received ultrasonic signal corrected by effective pressure increases with the increase of hydrate saturation; (4) the 100 kHz impedance modulus and corrected fluctuation amplitude of ultrasonic signal can be treated as effective electrical and acoustic characteristic parameters, respectively, for analyzing and establishing the relationships between the hydrate saturation and them. The apparatus developed in this work provides a necessary condition for future simulation experiments and parameter detection of hydrate-bearing complex sediments, and the proposed effective electrical and acoustic characteristic parameters provide a basis for establishing hydrate saturation calculation models.
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