Using 3-D Seismic Coherency...Cut Bank Field, Montana. Digital Download

GC0101D. Using 3-D Seismic Coherency and Stratal Surfaces to Optimize Redevelopment of Waterflooded Reservoirs, Cut Bank Field, Montana, by M. V. DeAngelo and B. A. Hardage. 24 p., 17 figs., 2001. doi.org/10.23867/gc0101D.

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About This Publication
The goal of this study was to improve results of an ongoing waterflood program in Glacier County, Montana, using 3-D seismic data collected over an 8-square-mile section of Cut Bank field. The 3-D data clearly delineated the presence of a major incised-valley system associated with the reservoir interval and revealed further information about reservoir compartmentalization that was not readily obtainable by conventional offset drilling. As a result of this study, five new proof-of-concept wells were drilled, four of which encountered reservoir-quality sand. Research was funded by MSR Exploration, a member of the Bureau's Exploration Geophysics Laboratory Industrial Associates.


ABSTRACT
In a 3-D seismic survey, we acquired data over an 8-mi² section of Cut Bank field, located on the west flank of Sweetgrass Arch in Glacier County, Montana. The main objective of the study was to improve the results of an ongoing waterflood program. The targeted reservoirs were an alluvial braided-stream system having a gross sand thickness of 20 to 25 ft. These reservoirs were deposited as incised-valley systems that are now at a depth of approximately 3,000 ft. Because clay plugging of abandoned channels is a major impediment to reservoir sweep, we thought that seismic-attribute analysis would help determine the aerial distributions of important facies within the reservoirs.

Traditional horizon-slice imaging of seismic reflection amplitudes suggested the presence of two possible incised-valley systems at two different depth intervals. Coherence analysis of reflection waveshapes more clearly defined these two incised-valley systems, and possibly three more, each at different depths.

We used an integrated interpretation approach to define these thinbedded fluvial channels laterally and vertically. We used coherence technology to identify the lateral extents of incised-valley systems, followed by stratal-surface interpretation techniques to determine the facies distributions within thin-bedded sequences deposited in these incised valleys.

Keywords: coherency, Cut Bank, incised valley, seismic amplitude, strata! surface, thin bed, waterflood

CONTENTS

Abstract

Introduction

Data Acquisition

3-D Coherency Imaging of Channel Systems

Wells and Facilities

VSP Calibration of 3-D Seismic Data

Stratal Surface Imaging of Channel Systems

Validation

Conclusions

Acknowledgments

References

Figures

1. Regional and depositional settings of Cut Bank field

2. Type log from UNOCAL well SCCBSU No. 51-6

3. Structure-contour map of base of Cut Bank Sandstone

4. 3-D seismic survey design, Cut Bank field

5. Calculation of continuity attributes

6. Time slice across amplitude volume at 432 ms

7. Time slice across amplitude volume at 482 ms

8. Time slice across coherence volume at 360 ms

9. Time slice across coherence volume at 432 ms

10. Time slice across coherence volume at 482 ms

11. Time slice across coherence volume at 570 ms

12. Time slice across coherence volume at 600 ms

13. Well distribution within the 3-D seismic study area

14. Correlation between 3-D seismic reflection character and VSP reflection character

15. Vertical seismic section along inline 200, displaying upper, mid-, and lower bounding stratal surfaces

16. Average absolute amplitude of upper Cut Bank sand unit

17. Average absolute amplitude of lower Cut Bank sand unit


Citation
DeAngelo, M. V., and Hardage, B. A., 2001, Using 3-D Seismic Coherency and Stratal Surfaces to Optimize Redevelopment of Waterflooded Reservoirs, Cut Bank Field, Montana: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 0101, 24 p. doi.org/10.23867/gc0101D.