Experimental study on dynamic acoustic characteristics of natural gas hydrate sediments at different depths

Abstract

Acoustic properties are important geophysical parameters, compared to resistivity, pore water and other parameters that need to be obtained through drilling, the acoustic wave velocity of hydrate deposits is much easier to obtain. Therefore, the study of acoustic characteristics of hydrate reservoir is the basis for geophysical exploration and resource evaluation for hydrates. In this study, an experimental apparatus was developed to measure dynamic P- and S-wave velocity of gas hydrate bearing sediment. The effect of sensitivity factors including hydrate saturation, confining pressure, and reservoir solid phase particle size on the acoustic characteristics of hydrate reservoir were explored. The experimental results showed that the longitudinal and transverse wave velocities of natural gas hydrate rock samples correlated positively with hydrate saturation and confining pressure and the particle size of the solid phase exhibited little effect on the vertical and horizontal wave velocity of the gas hydrate reservoir. The results of this study indicated that the compression factor of different rock samples is the main factor affecting the vertical and horizontal wave velocity of the reservoir through mechanical experiments. At the same time, acoustic experiments and computed tomography results revealed the existence of different contact modes between natural gas hydrate and sediment particles under different saturations. Furthermore, the possibility of detecting the microscopic distribution of hydrates in sediments by acoustic waves was verified. The data can be used in well logging to determine hydrate saturation and other properties of hydrate bearing formations.