Abstract
At present, attenuation characteristics of hydrate applicable to the seismic frequency band are still controversial. In this study, the dispersion and attenuation characteristics of hydrate in different occurrence modes were defined from the mesoscale perspective, and the saturation of hydrate in the study area is estimated. Based on effective medium theory and cementation theory, the skeleton elastic modulus of the sedimentary layer was obtained in the present study. The variation of P-wave attenuation with hydrate saturation was obtained by the patchy-saturation theory. P-wave attenuation increased with saturation when hydrate occurred in the suspension mode. P-wave attenuation decreased with saturation when hydrate occurred in the particle-contact or cementation mode. The particle-contact mode and cementation mode hydrate made the P-wave attenuation peak shift to the right. The influence of the cementation mode on attenuation was greater than that of the particle-contact mode. The conclusions of this study are applicable to the frequency range of seismic exploration, thus solving the problems of hydrate saturation prediction and resource quantity calculation assessment in the study area.
Highlights
Gas hydrate, known as “combustible ice,” is a kind of ice-like crystalline substance formed by natural gas and water under high pressure and low temperature, distributed in deep-sea sediments or permafrost soil
Three hydrate models were developed based on the patchy-saturation theory applicable at the mesoscale (White, 1975), and the relationships between hydrate saturation and dispersion and attenuation were obtained for different models
The theoretical relationships between the dispersion and attenuation of the three models and the hydrate saturation were derived from a mesoscale perspective for the first time
Summary
Known as “combustible ice,” is a kind of ice-like crystalline substance formed by natural gas and water under high pressure and low temperature, distributed in deep-sea sediments or permafrost soil. Gas hydrate has attracted much attention because of its great importance regarding energy, climate, environment, and disasters. The effect of gas hydrate on the velocity of seismic waves has been well understood. Various theoretical or experimental models have been proposed to estimate hydrate saturation by linking hydrate saturation with velocity (Wyllie et al, 1956; Wood et al, 1994; Lee et al, 1996; Helgerud et al, 1999). The common conclusion is that P-wave and S-wave velocities increase with hydrate saturation. Available theoretical formulae have different conditions of applicability. In areas without well data, it is not possible to calibrate theoretical formulae to guarantee the accuracy of hydrate saturation estimates. Alternative methods for hydrate saturation estimation are required
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