Internal structure of hydrated sediments and BSR as seismic evidence of free gas trapping by hydrate zone

摘要

The gas hydrate zone (GHZ) is identified on a seismic section by appearance of anomalous acoustic reflector which runs parallel to sea bed (Ref. 1). This bottom simulating reflector (BSR) is a result of velocity contrast between overlying gas hydrate (high velocities) and underlying sediments possibly containing free gas.In conventional model we assume that pore space is filled with hydrate and hence velocity contrast give rise to strong BSR. Ecker et al (1996) proposed two models of hydrate formation depending upon hydrate location within rock frame. In first model, hydrate cement grain contacts (reinforcing sediments) while in other model hydrate is located away from grain contacts. The density and seismic velocity in hydrate zone will depend upon percentage of hydrate, water and gas in pore space. The permeability will depend upon cementation of grain contacts by hydrates.