3-D Seismic Stratal-Surface Concepts Applied to the Interpretation of a Fluvial Channel System

GC9801. 3-D Seismic Stratal-Surface Concepts Applied to the Interpretation of a Fluvial Channel System Deposited in a High-Accommodation Environment, by B. A. Hardage and R. L. Remington. 15 p., 15 figs., 1998. ISSN: 0082-3309: Print.

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ABSTRACT
A fundamental thesis of seismic stratigraphy is that seismic reflections follow impedance contrasts that coincide with stratal surfaces, which are surfaces where depositional processes occur at a fixed moment in geologic time. This stratal-surface concept is used herein to image a narrow (width -300 ft), thin, fluvial channel system that is embedded within a seismic reflection peak. The peak reflects from a large (about 2- x 2-mi) area where nonchannel facies dominate its waveshape. The targeted channel facies are confined to an interval that vertically spans less than 30 ft. According to principles of seismic stratigraphy, four conformable seismic stratal surfaces that pass through the interior of this channel sequence were constructed across a 2- x 2-mi (approximately) area of a 3-D seismic-data volume. The channel images portrayed on these seismic horizons, which were spaced at vertical increments of 2 ms, illustrate the principle that seismic attributes viewed on seismic stratal surfaces provide valuable images of facies distributions within thin-bed sequences and help seismic interpreters segregate channel facies from nonchannel facies. These stratal-surface interpretations of the fluvial system were then integrated to create a thin (8-ms-kck), stratal-bounded seismic-data window that spans the short geologic time period during which the targeted fluvial depositional system was active. Seismic-attribute calculations within this stratalbounded analysis window improve parts of the channel image by integrating the facies information from all stratal surfaces into a unified seismic attribute that vertically spans the total depositional sequence. A comparison is made between channel images on seismic stratal surfaces that are conformable to two different reference surfaces, one reference surface being positioned below the targeted fluvial system and the second reference surface being above the h-bed channels. This comparison supports the premise that seismic interpreters should extrapolate stratal surfaces both upward and downward across a thin-bed target to optimize the image of that target.

Keywords: seismic stratigraphy, stratal surfaces, thin-bed interpretation

CONTENTS

Abstract

Introduction

Color Bar Used for Data Displays

Surface View of Targeted Fluvial System

Vertical Views of Channel and Nonchannel Seismic Facies

Crossline 174

Crossline 200

Crossline 222

Stratal-Surface Images of Channel Systems

Stratal-Bounded Seismic Analysis Windows

Combining Upward and Downward Extrapolations of Seismic Stratal Surfaces to Improve Thin-Bed Interpretation

Conclusions

Acknowledgments

References

Figures

1. 3-D seismic image of the targeted thin-bed Miocene fluvial channel system

2. Data window from crossline 174 centered on the northern, smaller channel system

3. Data window from crossline 174 centered on the southern, larger channel system

4. Data window from crossline 174 showing stratal surfaces that traverse the northern, smaller channel system

5. Data window from crossline 174 showing stratal surfaces that traverse the southern, larger channel system

6. Data window from crossline 200

7. Data window from crossline 200 showing stratal surfaces that traverse channel facies

8. Data window from crossline 222 centered on selected point-bar facies

9. Data from crossline 222 showing stratal surfaces that traverse point-bar facies

10. Reflection-amplitude behavior on stratal surface A. which is 92 ms above, and conformable to, the selected reference surface

11. Reflection-amplitude behavior on stratal surface B. which is 90 ms above, and conformable to, the selected reference surface

12. Reflection-amplitude behavior on stratal surface C. which is 88 ms above, and conformable to, the selected reference surface

13. Reflection-amplitude behavior on stratal surface D. which is 86 ms above, and conformable to, the selected reference surface

14. Average amplitude of reflection peaks in a thin, stratal-bounded window spanning the targeted Miocene fluvial sequence

15. Location of reference-surface 2 on crossline 200

Citation
Hardage, B. A., and Remington, R. L., 1998, 3-D Seismic Stratal-Surface Concepts Applied to the Interpretation of a Fluvial Channel System Deposited in a High-Accommodation Environment: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 98-1, 15 p.