Porosity estimation from pre-stack seismic data in gas-hydrate bearing sediments, Krishna-Godavari basin, India

Abstract

There exist several empirical and statistical methods for estimating porosity from post-stack seismic data. Here we implement and demonstrate a method for direct estimation of porosity from pre-stack seismic data. Rather than solving for acoustic impedance and then mapping those to porosity, we estimate porosity reflectivity. We demonstrate our approach with an application to 2D seismic dataset from Krishna-Godavari basin, which is inverted directly for porosity by simultaneous inversion of angle-stacks. The total porosity estimated from the density log for the depth interval of 1059–1224 m ranges from 49 to 85%. This relationship is used as an input for porosity inversion from the 2D pre-stack seismic data of gas hydrate bearing sediments. Our result images two distinct gas hydrate saturate zones in the porosity image; they are in close agreement with interpretations based on characterization of fractured filled gas hydrate saturation. The porosity along our 2D multichannel seismic section within the time interval of 1450–1615 ms ranges from 50 to 75% within the gas hydrate bearing sediments and unconsolidated sediments below the bottom simulating reflector. The water-bearing silty/clay sediments are characterized by porosity values of about 60–70%. The results demonstrate that the proposed approach is a fast and reliable method for estimating porosity directly from seismic data.