An Inversion Algorithm for Gas Hydrate Quantification
Abstract
The presence of gas hydrate in oceanic sediments increases the velocity and attenuation of the composite medium. The effects of hydrate saturation on compressional and shear wave velocities and their attenuations are different. These effects depend on the sediment microstructure, composition, the level of hydrate saturation and also the mode of hydrate formation in the pore space (inclusions vs connected). Using these parameters, we predict the velocities and attenuations of the sediments without hydrate, and thereby quantify hydrate saturation as deviation from these predicted velocities and attenuation factors. The influence of different parameters used and the variation of the predicted velocities and attenuations with frequency are studies using field and laboratory based datasets. Based on these studies we have developed an inversion algorithm to predict the gas hydrate saturation from velocities (Vp and Vs) and attenuation factors (Qp-1 and Qs-1) using porosity and physical parameters of the minerals constituting the sediment. Uncertainties in the estimates of hydrate saturation were quantified by testing the method on different datasets with accurately known parameters and corresponding estimated uncertainties. The algorithm will give hydrate saturation along with uncertainty. Using velocities and attenuation factors, the present method can predict the hydrate saturation accurately. The uncertainty in hydrate saturation is estimated to be less than 5% in usual situations. The method is applied to velocity sections estimated from OBS and multi-channel seismic data from the Storegga slide area, offshore Norway and offshore Svalbard. The method is also tested on velocity and attenuation measurements at seismic frequencies using a resonant column apparatus.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFMOS51B0850C
- Keywords:
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- 3025 Marine seismics (0935);
- 5102 Acoustic properties;
- 8105 Continental margins and sedimentary basins