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Scientific Investigations Report 2008–5219

Models for Gas Hydrate-Bearing Sediments Inferred from Hydraulic Permeability and Elastic Velocities

By Myung W. Lee

Abstract

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Elastic velocities and hydraulic permeability of gas hydrate-bearing sediments strongly depend on how gas hydrate accumulates in pore spaces and various gas hydrate accumulation models are proposed to predict physical property changes due to gas hydrate concentrations. Elastic velocities and permeability predicted from a cementation model differ noticeably from those from a pore-filling model. A nuclear magnetic resonance (NMR) log provides in-situ water-filled porosity and hydraulic permeability of gas hydrate-bearing sediments. To test the two competing models, the NMR log along with conventional logs such as velocity and resistivity logs acquired at the Mallik 5L-38 well, Mackenzie Delta, Canada, were analyzed. When the clay content is less than about 12 percent, the NMR porosity is “accurate” and the gas hydrate concentrations from the NMR log are comparable to those estimated from an electrical resistivity log. The variation of elastic velocities and relative permeability with respect to the gas hydrate concentration indicates that the dominant effect of gas hydrate in the pore space is the pore-filling characteristic.

Version 1.0

Posted December 2008

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Suggested citation:

Lee, M.W., 2008, Models for gas hydrate-bearing sediments inferred from hydraulic permeability and elastic velocities: U.S. Geological Survey Scientific Investigations Report 2008–5219, 14 p.



Contents

Abstract

Introduction

Principles of Nuclear Magnetic Resonance

Log Analysis

Theoretical Models

Discussion

Conclusions

References Cited

Appendix A. Permeability Model

Appendix B. Cementation Theory

Appendix C. Three-Phase Biot-Type Equation

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