3-D Seismic Interpretation of Deep, Complex Structures

GC9901. 3-D Seismic Interpretation of Deep, Complex Structures in the Delaware Basin, West Texas, by B. A. Hardage, V. M. Pendleton, and G. B. Asquith. 42 p., 31 figs., 1 table, 1999. ISSN: 0082-3309: Print.


To purchase this publication as a PDF download, please order GC9901D.



ABSTRACT
A multidisciplinary reservoir-characterization study of the Ellenburger Group was conducted over a 176-mi² 3-D seismic grid in Pecos, Reeves, and Ward Counties in the southern Delaware Basin of West Texas. The study area covered Lockridge, Waha, and West Waha fields and parts of Worsham-Bayer and Coyanosa fields, which have produced 1.3 trillion standard cubic feet of natural gas since their discoveries in the 1960's. Seismic time-structure and depth maps were generated for the tops of the Bone Spring-3, Mississippian, Devonian (Woodford), and Ellenburger. The focus of the study was to determine whether productive Ellenburger facies could be detected and mapped by using surface-recorded seismic data. No seismic attribute could be found, however, that exhibited any significant correlation with Ellenburger production. Systems of complex faults were interpreted across the 176-mi² 3-D image space.

The structural maps that were created are thought to be some of the most accurate depictions of the subsurface structure that are publicly available in this area of the Delaware Basin. Particular attention was given to documenting the overturned bedding and repeated sections that are associated with the interpreted fault systems. Both well log and 3-D seismic evidence of these tectonic folds and repeated reverse faults is presented. Natural gas production in the Lockridge-Waha region seems to be directly related to fracturing. The best gas production in Ellenburger, Devonian (Thirtyone), and Mississippian reservoirs in this study area occurs where wells are positioned close to faults and tends to increase as fault displacement and stratal distortion increase. The best production in the Lockridge-Waha region seems to be associated with reverse faults and with overturned sections. Wells should therefore be sited where they will penetrate the maximum number of fractured strata. From a 3-D seismic interpretation perspective, the requirement for siting productive wells is to place the well bore where seismic data allow an interpreter to infer that significant stratal movement and distortion have occurred because these rock deformation processes are indirect, but valuable, indicators of fracturing.

Keywords: Delaware Basin, Ellenburger, overturned beds, repeated sections, reverse faults, 3-D seismic


CONTENTS

Abstract

Introduction

3-D Seismic Data Acquisition and Processing

Seismic-Based Time-Structure Maps

Time-to-Depth Calibration

Acoustic-Log Control

Type Logs

Synthetic Seismogram Calibration of the 3-D Seismic Image

Deviated Wells

Low-Frequency Images and Fault Enhancement

Amplitude Attributes

Seismic-Based Depth Maps

Fault Styles

Overturned Beds

Simpson Example (Well 78)

Devonian Example (Well 63)

Reverse Faults and Repeated Sections

Simpson Example (Well 72)

Relation of Productive Facies to Faults

Seismic Isochron Maps and Their Tectonic Implications

New Geologic Information Provided by Lockridge-Waha 3-D Seismic

New Structural Insights

High-Potential Drilling Areas

Conclusions

Acknowledgments

References

Figures

1. Location map of study area

2. Stratigraphic column of the Delaware Basin

3. Top of Bone Spring-3 structure interpreted from Lockridge-Waha 3-D seismic data

4. Top of Mississippian structure interpreted from Lockridge-Waha 3-D seismic data

5. Top of Devonian (base Woodford) structure interpreted from Lockridge-Waha 3-D seismic data

6. Ellenburger structure interpreted from Lockridge-Waha 3-D seismic data

7. Traveltime-vs-depth behavior from 17 check-shot wells near Lockridge-Waha 3-D seismic survey

8. Traveltime-vs-depth behavior measured in four check-shot wells inside Lockridge-Waha 3-D seismic grid

9. Example synthetic seismogram calculation

10. Example of synthetic seismogram correlation with 3-D seismic image

11. Unfiltered and uninterpreted version of crossline 460

12. Uninterpreted version of crossline 460 after 3-D data are filtered to emphasize frequency content in lowest octave of the signal spectrum

13. Unfiltered and uninterpreted version of inline 970

14. Uninterpreted version of inline 970 after 3-D data are filtered to emphasize frequency content in lowest octave of the signal spectrum

15. RMS amplitude of Ellenburger reflection events as defined by full-bandwidth 3-D data volume

16. RMS amplitude of Ellenburger facies in low-frequency data volume

17. Seismic-based depth map of top of Bone Spring-3

18. Seismic-based depth map of top of Mississippian

19. Seismic-based depth map of top of Devonian (base Woodford)

20. Seismic-based depth map of top of Ellenburger

21. Example of folded Simpson section, well 78

22. Conceptual diagram showing apparent bed thickening caused by overturned bedding

23. Acoustic-neutron crossplot of typical Ellenburger section in Lockridge-Waha area

24. Acoustic-neutron crossplot of interval of well 78 incorrectly defined as Ellenburger

25. Seismic section passing through well 78

26. Logs showing overturned Devonian section observed in well 63

27. Seismic section passing through overturned Devonian section documented in well 63

28. Acoustic and gamma-ray logs recorded in well 72

29. Vertical section from 3-D seismic volume that passes through well 72

30. Isochron map of Ellenburger to Mississippian interval

31. Isochron map of Bone Spring-3 to Mississippian interval

Table

1. Velocity check-shot control


Citation
Hardage, B. A., Pendleton, V. M., and Asquith, G. B., 1999, 3-D Seismic Interpretation of Deep, Complex Structures in the Delaware Basin, West Texas: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 99-1, 42 p.