Model studies of ocean bottom seismometer experiment for gas-hydrateexploration

摘要

The P- and S-wave velocities of gas hydrates and free gas-bearing sediments and obtain the travel-time response for suitably spaced ocean bottom seismometers (OBS) on sea floor are model. The different models are presented with contrasting physical properties which produce the travel time curves corresponding to the gas hydrate and free gas layers for varying source-receiver offsets of the OBS. 2D ray tracing is done on models of different configuration, i.e. varying depths of sea floor, gas hydrate zone (GHZ) and free gas zone (FGZ) with the same sediment thickness. The best representative model is selected for each case, which produces the significant ray bending and travel time skips at contrasting velocity horizons of gas hydrate-bearing sediment layer underlain by significantly low velocity layer of free gas. Our results indicate that OBS should be deployed at a minimum of 5 km separation for getting better travel time response for GHZ and FGZ. The present exercise aims to provide some synthetic data that could be useful in deriving a physical model and in planning future OBS experiments for gas-hydrate exploration.