Seismic amplitude versus offset analysis of gas hydrates

We describe the application of AVO (Amplitude Versus Offset). analysis and high resolution velocity analysis to evaluate the elastic properties of Bottom Simulating Reflectors located in the South Shetland margin and in the South Chile offshore. Two marine seismic data sets are available for the study and were subjected to a full amplitude-preserved processing. This presented some difficulties due to the presence of noise related to the bad weather conditions during the acquisition. For this reason, after array directivity compensation and geometrical spreading correction, surface consistent amplitude corrections were applied and particular attention was given to the picking of the AVO trend of the target reflectors. This AVO has been used for a single interface elastic inversion of the PP reflection coefficient. The results given by high resolution velocity analysis, based on the a priori estimation of the wave let, and by AVO inversion indicate that both the South Chile and the South Shetland Bottom Simulating Reflectors are associated with interfaces showing high P-wave velocity (Vp) in the upper medium, followed by a consistent drop in Vp and in VpNs ratio in the lower medium. These results are consistent with the presence of a layer fully saturated and consolidated by gas hydrates overlying unconsolidated sediments with free gas (partial) saturation.