Laboratory measurements on gas hydrates and bubbly liquids using active and passive low-frequency acoustic techniques.

Abstract

The unique molecular structures of gas hydrates result in curious acoustic properties, which have yet to be adequately described. Understanding the acoustic behavior of stable and dissociating gas hydrates in liquids is vital for their localization and quantification using seismic or echosounding techniques. Further, with improved characterization of the acoustic properties of gas hydrates and bubbly liquids containing methane gas, acoustic methods may become an invaluable tool for monitoring hydrate dissociation and determining the magnitude of its effects on climate change. Acoustic properties of gassy substances are known to have a strong dependence on excitation frequency; however, tabulated values of hydrate material properties are most often measured in the frequency range of hundreds of kilohertz, while natural hydrate deposits and gas seeps are typically surveyed at seismic frequencies several orders of magnitude below laboratory measurement frequencies. This presentation details laboratory experiments in which a low-frequency (10 Hz–10 kHz) acoustic resonator apparatus was used to measure (a) sound speeds of bubbly liquids containing ideal and real gases and (b) bulk moduli and dissociation pressures of natural structure I and structure II gas hydrate samples. [Work supported by the Office of Naval Research.]