Acoustic characteristics on clayey-silty sediments of the South China Sea during methane hydrate formation and dissociation

Acoustic wave propagation can be used to detect hydrate reservoirs due to their unique characteristics in different media. Gas hydrate solids in reservoir pores exhibit higher wave velocities compared to pore fluids like seawater and free gas. Accurately predicting the abundance of hydrate reservoirs under different effective stress conditions is crucial for evaluating the exploitation value of hydrate reservoirs. In this study, the wave velocity of sediments was measured using two orthogonal S-waves for the first time, and the differences in S-wave velocities were used to characterize the anisotropy of the sediments. The results show that 1) a threshold value of hydrate saturation exists in clayey-silty sediments of the South China Sea, causing the wave velocity to show a trend of slow-then-fast, a new hydrate growth model was proposed to explain this change. 2) the growth pattern and occurrence type of hydrate play a dominant role in wave velocity. 3) hydrate can change sediment anisotropy, with higher hydrate saturation leading to a more isotropic sediment. 4) effective confining pressure can enhance wave velocity by altering the sediment skeleton. Finally, based on experimental data, an empirical formula was established and used to estimate hydrate saturation under different effective confining pressures.