Elastic properties of gas hydrate-bearing sediments

Downhole-measured compressional- and shear-wave velocities acquired in the Mallik 2L-38 gas hydrate research well, northwestern Canada, reveal that th e dominant effect of gas hydrate on the elastic properties of gas hydrate-b earing sediments is as a pore-filling constituent. As opposed to high elast ic velocities predicted from a cementation theory, whereby a small amount o f gas hydrate in the pore space significantly increases the elastic velocit ies, the velocity increase from gas hydrate saturation in the sediment pore space is small. Both the effective medium theory and a weighted equation p redict a slight increase of velocities from gas hydrate concentration, simi lar to the field-observed velocities; however, the weighted equation more a ccurately describes the compressional- and shear-wave velocities of gas hyd rate-bearing sediments. A decrease of Poisson's ratio with an increase in t he gas hydrate concentration is similar to a decrease of Poisson's ratio wi th a decrease in the sediment porosity Poisson's ratios greater than 0.33 f or gas hydrate-bearing sediments imply the unconsolidated nature of gas hyd rate-bearing sediments at this well site. The seismic characteristics of ga s hydrate-bearing sediments at this site can be used to compare and evaluat e other gas hydrate-bearing sediments in the Arctic.