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Scientific Investigations Report 2013–5141

Comparison of Methods for Predicting Shear-Wave Velocities of Unconsolidated Shallow Sediments in the Gulf of Mexico

By Myung W. Lee

Thumbnail of and link to report PDF (2.76 MB)Abstract

Accurate shear-wave velocities for shallow sediments are important for a variety of seismic applications such as inver-sion and amplitude versus offset analysis. During the U.S. Department of Energy-sponsored Gas Hydrate Joint Industry Project Leg II, shear-wave velocities were measured at six wells in the Gulf of Mexico using the logging-while-drilling SonicScope acoustic tool. Because the tool measurement point was only 35 feet from the drill bit, the adverse effect of the borehole condition, which is severe for the shallow unconsolidated sediments in the Gulf of Mexico, was mini-mized and accurate shear-wave velocities of unconsolidated sediments were measured. Measured shear-wave velocities were compared with the shear-wave velocities predicted from the compressional-wave velocities using empirical formulas and the rock physics models based on the Biot-Gassmann theory, and the effectiveness of the two prediction methods was evaluated. Although the empirical equation derived from measured shear-wave data is accurate for predicting shear-wave velocities for depths greater than 500 feet in these wells, the three-phase Biot-Gassmann-theory -based theory appears to be optimum for predicting shear-wave velocities for shallow unconsolidated sediments in the Gulf of Mexico.

First posted August 30, 2013

For additional information contact:
Director, Central Energy Resources Science Center
U.S. Geological Survey
Box 25046, MS-939
Denver Federal Center
Denver, CO 80225-0046
http://energy.usgs.gov/

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Suggested citation:

Lee, M.W., 2013, Shear wave velocities of unconsolidated shallow sediments in the Gulf of Mexico: U.S. Geological Survey Scientific Investigations Report 2013–5141, 11 p., http://pubs.usgs.gov/sir/2013/5141/.



Contents

Acknowledgments

Abstract

Introduction

Descriptions of Data

Biot-Gassmann Theory with Consolidation Parameter

Measured S-wave Velocity

Predicting S-wave Velocity

Results and Discussion

Summary and Conclusions

References


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