abstract
The second gas hydrate expedition drilled 13 sites in northern South China Sea and recovered a large amount of gas hydrate. The logging data and core analysis indicate that the gas hydrate occurs as solid nodules, disseminated within pore spaces of sediments and fracture fillings in veins. In this study, we examine two sites (sites 08 and 16), where gas hydrates occur both near the BSR and near the surface. We use the mesoscopic-loss mechanism to study the reflection coefficient versus frequency at BSR in seismic frequency band. When the seismic wave passes through the pore-filling gas hydrate sediments, the high frequency energy is much reduced and the low frequency energy of reflected waves at BSR is strong. When the seismic wave passes through the fracture-filling gas hydrate sediments, the high frequency wave is easily propagated and its reflected energy at BSR is strong. This difference of these at BSR between two types of gas hydrate contained sediments can be utilized to distinguish the gas hydrate morphology. The seismic data in northern South China Sea is analyzed and the results correspond well with the forward modeling approach.
