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Scientific Investigations Report 2007-5264

Velocities and Attenuations of Gas Hydrate-Bearing Sediments

By Myung W. Lee

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Scientific Investigations Report
2007-5264 PDF (1.3 MB)
Abstract

Monopole and dipole logging data at the Mallik 5L-38, Mackenzie Delta, Canada, provide a challenge for sonic velocity and attenuation models used to remotely estimate pore-space gas hydrate content. Velocity and attenuation are linked, with velocity dispersion causing increased attenuation. Sonic waveforms for Mallik 5L-38, however, show no velocity dispersion in gas hydrate-bearing layers, yet are highly attenuated. Attenuation models applied to Mallik 5L-38 data are shown to be inconsistent with the observed velocity measurements, and therefore are suspect in their ability to predict gas hydrate content. A model explicitly linking velocity and attenuation data is presented, accurately predicting gas hydrate content from velocity data alone while demonstrating that the attenuation mechanisms at the Mallik 5L-38 site have not yet been identified.

Version 1.0

Posted December 2007


Suggested citation:

Lee, Myung W., 2007, Velocities and attenuations of gas hydrate-bearing sediments: U.S. Gelogical Survey Scientific Investigations Report 2007–5264, 11p.



Contents

Abstract

Introduction

Acknowledgments

Theory of Three-Phase Equation

Derivation of equation

Moduli of dry frame

Computation of moduli formed by grain and gas hydrate

Dissipation potential

Velocity and Attenuation Modeling

Real Data Example

Discussion

Velocity

Estimation of gas hydrate amounts using velocity

Attenuation

Comparison with other theories

Conclusions

References



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