Acoustic properties of hydrate-bearing sand samples: laboratory measurements (setup, methods, and results)

Abstract

Abstract A new system has been designed for laboratory physical modeling of hydrate-bearing sand samples and measuring their acoustic properties at different temperatures and pressures. The system includes a pressure vessel, units of temperature control, external pressure, and gas/liquid delivery, and a unit for measuring velocities of acoustic waves. Measurements are carried out in 10–50 mm high cylindrical specimens 30 mm in diameter. The system provides methane hydrate formation in sand samples and their acoustic measurements for as long as several days due to automatic control. Hydrate-bearing samples are prepared by pressurized methane injection into pores of wet sand and are exposed to several cooling/heating cycles to increase hydrate formation rates. Hydrate-bearing samples have been prepared and travel times of acoustic P and S waves have been measured in dozens of successful experiments. Acoustic data confirm the formation of hydrates, with the related increase in wave velocities to values about those in frozen sediments. The prepared gas hydrates are inferred to be of “cementing” type, i.e., they form as cement at the boundaries of mineral grains. The obtained velocities of acoustic waves show a positive linear correlation with hydrate contents in sand samples.