1. Pitfalls in seismic processing : The origin of acquisition footprint Sumit Verma, Marcus P. Cahoj, Bryce Hutchinson, Tengfei Lin, Fangyu Li, and Kurt J. Marfurt, The University of Oklahoma

2. Content 2 1.Introduction 2.Hypothesis and Methodology 3.Seismic Modeling i.Inadequate removal of groundroll ii.Incorrect velocity picking 4.Results 5.Conclusions IntroductionMethodologySeismic modelingResultsConclusions

3. Acquisition footprint refers to the imprint of acquisition geometry on the seismic amplitude time and horizon slices. Acquisition footprint can obstruct seismic amplitude/attribute interpretation. Commonly posed question: “How can one remove acquisition footprint?” Our focus: The illustration of the origin of footprint with seismic modeling. Practically: Studied a seismic dataset contaminated with acquisition footprint. Investigated possible causes of the generation of footprint on this dataset. 3 Introduction Introduction MethodologySeismic modelingResultsConclusions

4. 4 Study area Sources Receivers Survey Area  9 mi 2 0 40 20 Fold Fold Map Study area Texas USA Bin :110’ x 110’Introduction MethodologySeismic modelingResultsConclusions

5. 5 Motivation Seismic Amplitude Positive Negative Time (ms) 0 450 1 mi Curvature Positive Negative N 1 mi 250 Time slice at t = 420 ms Time (ms) 0Introduction MethodologySeismic modelingResultsConclusions

6. Inadequate removal of groundroll Improper velocity analysis causing the reflectors to be under/over corrected Not investigated in this study: far offset stretching of the wavelet Footprint – Hypotheses 8 IntroductionMethodology Seismic modelingResultsConclusions

7. Real seismic survey Simple 2D Seismic modeling 4 layers (acoustic) Real 3D survey geometry Model for dispersive groundroll (elastic) Synthetics with groundroll Inadequate suppression of groundroll Processing Velocity analysis Pick velocities 5% too fast Pick velocities 5% too slow Prestack Kirchhoff time migration Stack the synthetic data Compute geometric attributes Workflow 9 Hypothesis 1 Hypothesis 2 IntroductionMethodology Seismic modelingResultsConclusions Synthetics

8. Gridded a 2D geologic model and used the finite-difference method to solve the wave equation. We choose the velocity, density, and depth of the formations from well logs. 8 Modeling approach IntroductionMethodology Seismic modelingResultsConclusions

9. 9 Survey geometry Trace-offset relationship from 2D model applied to the 3D survey geometry. Offsets from 2D model redistributed in a 3D geometry.

10. Inadequate removal of groundroll Improper velocity analysis causing the reflectors to be under/over corrected Not investigated in this study: far offset stretching of the wavelet Footprint – Hypotheses 8 IntroductionMethodology Seismic modeling ResultsConclusions

11. Offset (ft) Groundroll modeling Depth (ft) IntroductionMethodology Seismic modeling ResultsConclusions

12. V P =4000 ft/s V P =5000 ft/s V P =8000 ft/s V P =6000 ft/s Offset (ft) Time (ms) 500 1500 Offset (ft) 8000 4000 Seismic Amplitude Positive Negative 0 Time (ms) 500 1500 0 0 Offset (ft) 8000 4000 0 Groundroll modeling Depth (ft) Groundroll only Groundroll+ reflectors IntroductionMethodology Seismic modeling ResultsConclusions

13. 13 Seismic Amplitude Positive Negative Time (ms) 500 1500 Offset (ft) 8000 4000 0 Time (ms) 500 1500 Offset (ft) 8000 4000 0 Groundroll modeling Groundroll+ reflectors After F-K filter IntroductionMethodology Seismic modeling ResultsConclusions

14. 14 Time (ms) 500 1500 0 1000 1 mi Curvature Positive Negative A A’ Stacked image – Groundroll Modeled data Time slice at t = 420 ms N IntroductionMethodologySeismic modelingResults Conclusions

15. Inadequate removal of groundroll Improper velocity analysis causing the reflectors to be under/over corrected Not investigated in this study: far offset stretching of the wavelet Footprint – Hypotheses 8 IntroductionMethodology Seismic modeling ResultsConclusions

16. Velocity picking - mute applied Time (ms) Semblance High Low 51018 Velocity *10 3 (ft/s) 080004000 Offset ft/s 400 800 1000 600 200 0 IntroductionMethodology Seismic modeling ResultsConclusions

17. 17 Velocity picking – 5% too fast velocity 400 800 1000 600 200 Semblance High Low 0 51018 Velocity *10 3 (ft/s) 080004000 Offset ft/s Time (ms) IntroductionMethodology Seismic modeling ResultsConclusions

18. 18 Velocity picking – 5% too slow velocity 400 800 1000 600 200 Semblance High Low 0 51018 Velocity *10 3 (ft/s) 080004000 Offset ft/s Time (ms) IntroductionMethodology Seismic modeling ResultsConclusions

19. 19 Stacked image – 5% fast velocity Seismic Amplitude 1 mi Time (ms) 400 800 0 1200 1600 2000 1 mi Curvature Positive N Time slice at t = 616 ms Negative Positive Negative IntroductionMethodologySeismic modelingResults Conclusions

20. 20 Stacked image – 5% slow velocity 1 mi Time (ms) 400 800 0 1200 1600 2000 Seismic Amplitude Positive Negative 1 mi Curvature Positive N Time slice at t = 616 ms Negative IntroductionMethodologySeismic modelingResults Conclusions

21. 21 Comparison Groundroll 5% too slow Real data IntroductionMethodologySeismic modelingResults Conclusions

22. Both improper removal of groundroll and incorrect velocity analysis can create artifacts in a seismic dataset Incorrectly picking velocities by a mere 5% can lead to significant effects in the data. Picking velocities too slow creates a close approximation of the undulatory feature seen in real data. Attributes can often exacerbate acquisition footprint. We believe that undulatory features in the Jean survey could be sourced by incorrect velocity analysis. 22 Conclusions IntroductionMethodologySeismic modelingResultsConclusions

23. Acknowledgement 23 Data courtesy Mike Burnett of TameCat LLC. AASPI consortium members. Thanks to AASPI consortium sponsors for financial support.

24. Thank you for your time. Questions? 24