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Three VSP Algorithms: Surface Seismic Transform, NMO and Migration Velocity Analyses

Three VSP Algorithms: Surface Seismic Transform, NMO and Migration Velocity Analyses. Yue Du Mark Willis, Robert Stewart AGL Research Day. April 2nd, 2014 Houston, TX. Talk outline. Motivation & introduction VSP has higher resolution, target oriented, small data volume

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Three VSP Algorithms: Surface Seismic Transform, NMO and Migration Velocity Analyses

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  1. Three VSP Algorithms: Surface Seismic Transform, NMO and Migration Velocity Analyses Yue Du Mark Willis, Robert Stewart AGL Research Day April 2nd, 2014 Houston, TX

  2. Talk outline • Motivation & introduction VSP has higher resolution, target oriented, small data volume • Three algorithms 1. Transforming VSP to surface seismic data; 2. Downward continuation of surface shots with joint NMO velocity analysis; 3. Residual moveout migration velocity analysis • Future work -Hess VSP survey

  3. 1. Transforming VSP to surface seismic records (Schuster , 2009) Part 1 Part 2

  4. Two-layer model simulation results Surface seismic shots Simulating shot from VSP 1.2D acoustic finite difference modeling 2.Seprate waveform convolution— without first arrivals 3.Artifacts—taper 4.Borehole receiver coverage Simulating shot from VSP with taper Reduced receiver coverage

  5. 2D & 3D simulation results Left – Actual surface shot Middle – simulated surface shot from the Part 1 Right – simulated shot from Part 2

  6. 2. Downward continuation with joint NMO analysis 1 Reflector A 2 Reflector B

  7. Downward continuation • Raw data • Downward continued data Reflection A Reflection A Reflection B Reflection B Reflection B Reflection B 7

  8. NMO correction and semblance spectra analysis • Before NMO correction • After NMO correction Reflection A Reflection A Reflection B Reflection B Reflection B Reflection B Receiver 2 Receiver 1 Receiver 1 Receiver 2 8

  9. 3. Migration velocity analysis V migration depth, m XOZ coordinates source X s O δ g O’ Tilted ellipse coordinates UO’V’ receiver U Reflector CIP Z XOZ coordinates X, m x

  10. The intersections of tilted migration ellipses Correct velocity depth, m source2 source3 source1 Receiver migration depth, m Slow velocity X, m Slow velocity source2 source3 source1 Correct velocity depth, m Receiver Source X, m X, m

  11. Residual moveout after migration RMO for a CIG Unstacked CIG Slow velocity depth, m Depth, m Correct velocity Fast velocity receiver depth, m source x Source X, m

  12. VSP multi-layer model Modeling data with reflection events only 0 Receiver gather R1 1000 time, ms 2000 0 time, ms Shot gather for source x=0 1000 3000 2000 3000 4000 Source offset Receiver depth

  13. Downward continuation with joint NMO analysis • Pick RMS velocity • Interval velocity model True velocity model Estimated velocity model 13

  14. Migration velocity analysis RMO After Migration Vmig = Vtrue Velocity Model Tilted Ellipse RMOs 2600 A (Vlayer4=0.9Vtrue) Depth, m Depth, m A’ (Vlayer4=0.95Vtrue) 2700 B (Vlayer4=Vtrue) C (Vlayer4=1.05Vtrue) C’ (Vlayer4=1.1Vtrue) 2800 Receiver Depth, m Receiver Depth Velocity, m/s

  15. Summary • VSP geometry is asymmetric, thus it is hard to apply velocity analysis tools from surface seismic • The three algorithms can be used separately or together to help VSP analyses • Transforming to surface seismic records from VSP data has limitations

  16. Acknowledgements • Allied Geophysical Lab and its supporters • Halliburton • Thank you kindly Michele Simon and colleagues at Hess for contributing the 3D time-lapse Bakken data for our future research. We also express our appreciation to Richard Van Dok at Sigma3 for data preparation. Thank you！

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