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Prestack Waveform Inversion: an Onshore Application in the US Gulf Coast

Prestack Waveform Inversion: an Onshore Application in the US Gulf Coast. August Lau, Chuan Yin, Mike Greenspoon, Apache Corp; Anthony Vassiliou, GeoEnergy September 2007. Well to Seismic Tie.

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Prestack Waveform Inversion: an Onshore Application in the US Gulf Coast

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  1. Prestack Waveform Inversion: an Onshore Application in the US Gulf Coast August Lau, Chuan Yin, Mike Greenspoon, Apache Corp; Anthony Vassiliou, GeoEnergy September 2007

  2. Well to Seismic Tie Well-to-seismic tie: zero-offset synthetic and PSTM final stack. Displayed panels are (L to R): gamma-ray log, resistivity log, sonic log, bulk density log, full-stack overlaid with zero-offset synthetic, cross-correlation of the synthetic to surface seismic.

  3. Post-stack Rock Properties

  4. Pay sand has lower Vp / Vs and P- imp Pre-Stack Rock Properties Sand with Pay has Lower Vp / Vs Ratio and Lower P-impedance

  5. Workflow

  6. Input PSTM Gather (Left) and Modeled Gather

  7. Vp InitialFinal Vs InitialFinal Density InitialFinal Starting and Final Models

  8. Applications of Pre-Stack Inversion • Estimation of Vp, Vs, density, Zp, Zs and their uncertainties for fluid and lithology discrimination • Through calibration and interpretation, thickness estimation, net to gross estimation, porosity estimation • Interpretation of small-scale or localized features, such as narrow channels, slump faults, etc.

  9. Well F Well 3 Well A 2000’ Well B Well D Well C Well E ARB LINE Full Stack Amplitude Extraction

  10. Full Stack Main Producing Field Cross Section WELL F WELL A WELL B WELL C WELL E Horizon A Horizon B

  11. 5-20 Angle Stack Main Producing Field Cross Section WELL F WELL A WELL B WELL C WELL E Horizon A Horizon B

  12. Arbitrary Line-Interpreted Lithology Cube Main Producing Field Cross Section WELL F WELL A WELL B WELL C WELL E Horizon A Horizon B

  13. Well F Well 3 Well A 2000’ Well B Well D Well C Well E ARB LINE Vp/Vs Volume

  14. Well F Well 3 Well A 2000’ Well B Well D Well C Well E ARB LINE DZP

  15. Well F Well 3 Well A 2000’ Well B Well D Well C Well E ARB LINE DZS

  16. Inversion Technique Differences Major Differences between Pre-stack Waveform Inversion applied to gathers and angle-stack inversions: • Pre-stack waveform inversion is applied directly on gathers with NMO removed, preserving all amplitude, phase, offset information • Pre-stack waveform inversion is seismic data driven. Angle stack inversion commonly well log driven • Assuming long enough acquisition cable, pre-stack waveform inversion estimates directly Vp, Vs, density

  17. Inversion Technique Differences con’t. • Pre-stack waveform inversion can work with either only primary reflections or with both primary and multiple reflections • Pre-stack waveform inversion applied directly on gathers does not have to deal with the NMO stretch effect for long cables • Pre-stack waveform inversion makes use of interval velocities. • Pre-stack waveform inversion applied on gathers is not sensitive to starting low frequency Vp / Vs / density model

  18. Conclusions • Pre Stack Inversion is a faster, cheaper, and more accurate method than traditional well-based inversion techniques • Various output volumes can be calibrated with well control for net pay estimations • Prospects can be qualified with multi-cube interpretation • A detailed geologic input model is not necessary to produce results

  19. Acknowledgements • Seismic Data Courtesy of Seitel

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