AVO ANALYSIS

In order to evaluate the effects of the different hydrate deposition models on seismic reflection responses, we performed 1-D, elastic modeling using the Thompson-Haskell reflectivity method. All layers were assumed to be flat and approximately 300 meters thick. We used the previously-calculated, saturated velocities of the different hydrate models as input for the hydrate-saturated layer. The hydrate layer was overlain by a brine-saturated sandstone and underlain by either a brine-saturated sandstone layer or a gas-saturated sandstone layer. For the gas-saturated sandstone layer we chose a 50% gas saturation. The properties of theses layers were also calculated in the previous section (Figure 3). The configuration of the two different synthetic models, one model simulating the structure for hydrate overlaying brine, one simulating hydrate overlaying gas, can be seen in Figure 4. Both models were overlain by a thick water column.

 

model
Figure 4 Synthetic models for the hydrate structures. The left model shows the configuration for hydrate overlaying brine, the right shows hydrate over gas.

We generated synthetic seismograms for different hydrate saturation in the hydrate layer and compared the different seismic responses. Subsequently, in order to evaluate the actual amplitude behavior at the BSR, which is the bottom of the hydrate stability zone, we determined its AVO response using Zoeppritz equations.