1. King Field AVO Sensitivity to Reservoir Thickness and Amplitude Scaling Gregory A. Partyka and Philip J. Whitaker BP

2. Goal Illustrate the effect of: –thickness, –layer-stacking, and –amplitude scaling on AVO response.

3. Outline IntroductionIntroduction AVO Modelling Conclusions

4. King Field – Location

5. King Field – Amplitude Map 129-1 85-1 1 mile

6. King Field – AVO Map 129-1 85-1 Far - Near Amplitude 1 mile

7. 129-1 Well-Log Signature 8,440 3,180 2.29 8,810 3,480 2.34 7,750 4,105 2.13 TVD (ft) Vs (ft/s) Vp (ft/s) Den (g/cc) 0 1 2,000 4,000 AI Den Vs Vp 40,000 3 6,000 12,000 Core Samples Xplot Porosity Water Oil Sand Shale 43ft gross gas pay fining upward sharp basal contact; gradational top 129-1 Amplitude Map

8. 085-1 Well-Log Signature 9,340 4,395 2.37 9,025 4,780 2.21 9,340 4,860 2.20 10,160 4,375 2.40 10,015 4,930 2.40 TVD (ft) Core Samples Xplot Porosity Water Oil Sand Shale Vs (ft/s) Vp (ft/s) Den (g/cc) 10,000 1 2,000 4,000 AI Den Vs Vp 30,000 3 6,000 12,000 80ft gross gas pay interbedded sand-shale sharp basal and top contact 85-1 Amplitude Map

9. Outline Introduction AVO ModellingAVO Modelling –Half-Space –Tuning and Thickness –Amplitude Scaling Conclusions

10. Half-Space AVO 85-1 129-1 These signatures represent the individual half- space components that comprise the composite tuned reflection. Large amplitudes that increase with offset. Reflection Coefficient Angle of Incidence

11. AVO Modelling Half-Space Tuning and ThicknessTuning and Thickness energy, phase, and frequency slope and intercept Amplitude Scaling

12. Energy, Angle, and Thickness Simple reservoirs exhibit simple tuning characteristics. increasing thickness Angle of Incidence 01020304050 Energy Angle of Incidence 01020304050 Energy increasing thickness 129-1 85-1

13. The Tuning Curve 0 100 travel-time (ms) 200 1.0 reflection coefficients 0.1 0 100 travel-time (ms) 200 2 0 energy 0 100 travel-time (ms) 200 reflectivity amplitude energy

14. Phase, Angle, and Thickness increasing thickness Angle of Incidence 01020304050 Phase increasing thickness Angle of Incidence 01020304050 Phase 129-1 85-1

15. Phase and Tuning 180 -180 0 0 100 travel-time (ms) 200 1.0 reflection coefficients 0.1 0 100 travel-time (ms) 200 phase 0 100 travel-time (ms) 200 reflectivity amplitude phase

16. Frequency, Angle, and Thickness increasing thickness Angle of Incidence 01020304050 Frequency Angle of Incidence 01020304050 Frequency 129-1 85-1

18. AVO, Thickness, and Tuning AVO-Intercept 85-1 129-1 Gross Reservoir Thickness (ft) 0 708010090506040102030 EnergyVA Intercept 85-1 129-1 EnergyVA Slope Gross Reservoir Thickness (ft) 708010090506040102030 85-1 129-1 AVO-Slope

19. Thickness well-log measured thickness. seismic measured thickness. true-vertical thickness. reservoir thickness. + imaging problems imposed by structural complexity.

20. Thickness Considerations mt 1 mt 2 tvt 1 st 1 tvt 2 st 2 Case 1: Drilling Updip tvt 1 < mt 1 tvt 1 < st 1 Case 2: Drilling Downdip tvt 2 < mt 2 tvt 2 > st 2 reservoir thickness Where: mt = well-log measured thickness st = seismic-measured thickness tvt = true-vertical thickness

21. AVO and Amplitude Scaling

22. 85-1 129-1 Amplitude Scalar 1.61.81.41.01.22.0 EnergyVA Intercept 85-1 129-1 Amplitude Scalar 1.61.81.41.01.22.0 EnergyVA Slope using a constant 50ft thickness 85-1 129-1 AVO-Intercept AVO-Slope

23. Outline Introduction AVO Modelling ConclusionsConclusions

24. Conclusions AVO attributes are sensitive to: –thickness, –reservoir layer-stacking, and –amplitude scaling.

25. Suggestions Reservoir-specific modelling helps interpreters unravel and understand reservoir-specific AVO behaviour. Tuning and thickness can have a large effect on AVO response. Consistent amplitude scaling is important, particularly when: –integrating multiple overlapping or time-lapse seismic volumes. –comparing real and modelled AVO gathers.

26. King Field – UM70 Net Pay and AVO Far-Near Amplitude Map After 7 penetrations After 2 penetrations

27. Acknowledgments We wish to thank BP for allowing us to present this material. BP Unix Seismic Processing (USP) Team for providing the technical framework for creative thinking, algorithm development and implementation. –See www.freeusp.org for related material.