Estimating the amount of gas hydrate in marine sediments in the Blake Ridge area, southeastern Atlantic margin

A relative amount of gas hydrate in marine sediments can be estimated by use of either interval velocity or amplitude blanking in seismic profiles. Under the assumption of constant concentration of hydrate irrespective of porosity, the average bulk hydrate amounts for the lower portion of marine sediments above the bottom simulating reflector in the Blake Ridge area, south-eastern Atlantic Margin, is estimated to be about 8.7% of the sediments when using velocity analysis and about 10% when using amplitude blanking. Under the assumption of variable hydrate concentration proportional to the porosity, the estimate is about 8.1% when using velocity information and about 10% when using amplitude blanking.

The estimation method using amplitude is comparable to the estimation by interval velocity and provides a convenient way of quantitative classification of the degree of hydrate cementation. In the amplitude method, three classes of blanking are defined; class boundaries represent a change in reflection amplitude by a factor of 2, and the classes may be used to predict the amount of hydrate in bulk sediments.