ZHANG Huaiwen, CHENG Yuanfang, ZHU Haitao, SHI Jihui, HAN Xiuting
In order to understand the acoustic characteristics and differences of muddy siltstone hydrate sediment (MSHS) and siltstone hydrate sediment (SHS) in the shallow seabed of South China Sea, a simulation experiment is conducted to investigate the acoustic response characteristics of these two hydrate sediments with the ultrasonic detection technology. The results show that the acoustic velocities of these two hydrate sediments will increase with the increase of effective confining pressure. However, when the effective confining pressure increases to the effective confining pressure saturation point, the acoustic velocities of these two hydrate sediments will not change anymore. Meanwhile, with the increase of hydrate saturation, the effective confining pressure saturation points of these two hydrate sediments will also increase. The effective confining pressure saturation point of MSHS is higher than that of SHS and the difference is between 7-10 MPa. Under the same effective confining pressure, the larger the hydrate saturation, the faster the acoustic velocity for both hydrate sediments, showing a "slow-fast-slow" tendency. The 20%-40% of hydrate saturation is the fast increasing range of the acoustic velocity, with an increase over 22%. The acoustic velocity of MSHS is greater than that of SHS under the same experiment condition. Furthermore, the change of hydrate saturation and effective confining pressure have a great effect on the acoustic velocity of these two hydrate sediments, and acoustic velocity has a greater influence on MSHS than on SHS.
