GASSY SEDIMENT OCCURRENCE AND PROPERTIES - NORTHERN GULF-OF-MEXICO

Free gas is ubiquitous at shallow sediment depths of the northern margin of the Gulf of Mexico. Gassy sediment patches are between 250 and 500 m in horizontal size. Often the gassy layers are within 100 m from the sea floor and are only a few meters thick. Both biogenic and thermogenic gas hydrates have been recovered. Stability values of temperature and pressure indicate that hydrates can exist in water depths less than 500 m. Gassy sediment geocoustic parameter values are not well constrained because of a lack of concurrent measurements of acoustic properties and sediment gas content. For Gulf of Mexico gassy sediment, some reported in situ values of sound speed are reduced by an order of magnitude below values for water saturated sediments. More commonly, sound speed is reduced from water saturated sediment values by only 15 to 50 percent.