Abstract:
Bulk properties of gas hydrate-bearing sediment strongly depend on whether hydrate forms primarily
in the pore fluid, becomes a load-bearing member of the sediment matrix, or cements sediment
grains. Our compressional wave speed measurements through partially water-saturated, methane
hydrate-bearing Ottawa sands suggest hydrate surrounds and cements sediment grains. The three
Ottawa sand packs tested in the Gas Hydrate And Sediment Test Laboratory Instrument (GHASTLI)
contain 38(1)% porosity, initially with distilled water saturating 58, 31, and 16% of that pore space,
respectively. From the volume of methane gas produced during hydrate dissociation, we calculated
the hydrate concentration in the pore space to be 70, 37, and 20% respectively. Based on these hydrate
concentrations and our measured compressional wave speeds, we used a rock physics model to differentiate
between potential pore-space hydrate distributions. Model results suggest methane hydrate
cements unconsolidated sediment when forming in systems containing an abundant gas phase.
