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Gas Hydrate Exploration with 3D VSP Technology, North Slope, Alaska

Gas Hydrate Exploration with 3D VSP Technology, North Slope, Alaska

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Gas Hydrate Exploration with 3D VSP Technology, North Slope, Alaska

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  1. Gas Hydrate Exploration with 3D VSP Technology, North Slope, Alaska Donn McGuire, Anadarko Petroleum Corp. Steve Runyon & Tom Williams, Maurer Technology, Inc. Björn Paulsson, Alex Goertz & Martin Karrenbach, P/GSI Society of Exploration Geophysicists – 74th Annual Meeting October 14, 2004

  2. Outline • Introduction, background & objectives • Survey design • Acquisition & processing • Results & interpretation • Conclusions

  3. Introduction, background & objectives

  4. Methane Hydrate Project GoalsAlaska North Slope • Assess the areal extent of hydrate accumulation • Derive a geologic model of hydrate accumulation • Assess potential hydrate reserves • Determine the production capacity of hydrates

  5. Methane Hydrate Project Tasks • Drill, core, log and test one well (HOT ICE #1) • Evaluate core on site using a new mobile core lab • Assess geophysical characteristics using a 3D VSP • Complete and test most promising hydrate interval

  6. APC Locations Gas Hydrate Stability Zone Thickness Point Barrow Beaufort Sea 400m 600m 200m Prudhoe Bay Oil Field 0 Map courtesy of USGS

  7. Cirque #2 W.Kuparuk 3-11-11 NW Eileen State #2 Hot Ice (projected) W.Kuparuk 26-12-12 Gwydyr Bay Gwydyr Bay State-1 State-2 Reindeer Island-1 W. Sak #15 W. Sak #3 K.R.U. 1D-8 0 0 1000 500 2000 Depth (m) Depth (ft) 3000 1000 4000 1500 A’ A Prudhoe Bay Oil Field 2000 Generalized Cross Section SW NE Courtesy of USGS

  8. SW NE GENERALIZED STRATIGRAPHIC COLUMN, NORTH SLOPE, ALASKA Stratigraphic Column

  9. Hot Ice 2 FLUVIAL Hot Ice 3 Hot Ice 1 Lower Paleocene (Ugnu) Paleogeography Modfiied from Wemer, 1982 & NARS, 1990

  10. 2D Seismic Section Hot Ice Well Projected NW SE Top HSZ Base Permafrost Base HSZ Data courtesy of WesternGeco

  11. Introduction, background & objectives • Survey design

  12. Fold Calculations vs. Well Offset

  13. 130 Hz 2100 ft target 130 Hz 1800 ft target 200 Hz 2100 ft target 200 Hz 1800 ft target target velocity: 6500 ft/sec Fresnel Zone vs. Well Offset

  14. Surface Shotpoint Map Shotpoint interval increases from 120 ft at well to 175 ft at outer ring

  15. Introduction, background & objectives • Survey design • Acquisition & processing

  16. Summary of Acquisition Parameters • 1185 surface shotpoints in a circular array • 80 receiver levels at 25 ft spacing • 3 15 Hz OYO SMC1850 geophones per receiver: 1 vertical + 2 horizontal • 284,400 seismic traces recorded • Seismic source: Single AHV4 Vibroseis (62,000 lb) • Sweep parameters: 2 x 8 - 220 Hz 10 sec linear sweeps, 0.2 sec cosine taper • Well nominally vertical, 7” casing to 1,358 ft, open hole to 2,300 ft. TD

  17. Hot Ice Arctic Platform Drilling rig Crew quarters

  18. Receiver spool Receiver pods Receiver pods Survey tubing VSP Survey Equipment in the Drilling Room

  19. 3-Component receiver in survey pod

  20. Inflatable bladder in survey pod

  21. 8-14-60-80 Hz 8-14-150-200 Hz Z-10 Hydrate Z-9B Hydrate Z-9A Hydrate Base Permafrost Z-8C Hydrate Z-8B Free Gas Frequency Resolution of Hydrate Sands Cirque #2

  22. Vibrators for Surface Sources AHV4 (62,000 lb) vibrators provided by PGS Onshore

  23. Frequency (Hz) Power (dB) Frequency Spectrum of Recorded Energy spectrum from zero offset, near surface receivers

  24. Data Processing Steps • Receiver geometry • 3-Component orientation • Pick first breaks • Wavefield separation • Statics correction • Deconvolution • Amplitude recovery • Velocity computation • Kirchhoff prestack depth migration

  25. Before Rotation to XYZ: Shotpoint due North H1 H2 V 3-Component orientation

  26. After Rotation to XYZ: Shotpoint due North E N Z Minimized energy Maximized energy No change in energy 3-Component orientation

  27. Near Mid Far Raw Data at Near, Mid, and Far Offsets with AGC cased hole open hole First break picks

  28. Upgoing Wavefield with AGC cased hole open hole Near Mid Far Wavefield separation

  29. cased hole open hole Deconvolution Raw wavefield at 1500 ft. offset

  30. cased hole open hole Deconvolution Wavelet inversion at 1500 ft. offset

  31. 10000 8000 Velocity Computations Sonic data in upper half of wellbore are unreliable due to washouts First break picks possibly biased due to open hole interference (Note the reduced variance in the after-survey velocities) Sonic log and average 1D velocity profiles 3D velocity volume

  32. Introduction, background & objectives • Survey design • Acquisition & processing • Results & interpretation

  33. Comparison of VSP and Surface Seismic Surface data courtesy of BP and ConocoPhillips

  34. Synthetic Seismogram Hot Ice well Stack Traces Offset Traces P-Wave S-Wave Impedance Gamma Ray Density Poisson 1 2 Depth Time 1 - On offset gathers, the top and base of the in-situ sand below permafrost should have little change in reflectivity with offset. 2 - On stacked, zero phase data, this sand should have little reflectivity at the top and a weak to moderate peak at the base.

  35. Synthetic Seismogram Hot Ice well Stack Traces Offset Traces P-Wave S-Wave Impedance Gamma Ray Density Poisson Depth Time

  36. Offset Traces Stack Traces P-Wave Gamma Ray Density Poisson Impedance S-Wave Depth Time Synthetic Seismogram for Hydrate-bearing Sand

  37. Offset Traces Stack Traces P-Wave Gamma Ray Density Poisson Impedance S-Wave Depth Time Synthetic Seismogram for Hydrate-bearing Sand 1 2 • 1 - On offset gathers, the top of a hydrate-bearing sand should be a strong peak and the base should be a strong trough, both decreasing in amplitude with offset. • 2 - On stacked, zero phase data, this sand should have a strong peak at the top and little or no reflectivity at the base.

  38. 3D VSP Seismic Volume

  39. 3D VSP Seismic Volume with Well Logs Well log colorfill: Left: Vshale < 50% Right: Porosity > 15%

  40. 3D VSP Seismic Volume with Well Logs W E Well log colorfill: Left: Vshale < 50% Right: Porosity > 15%

  41. E-W Profile with Ugnu Plane W E Base Ugnu Plane Well log colorfill: Left: Vshale < 50% Right: Porosity > 15%

  42. E-W Profile with Ugnu Plane at Top of Sand A W E Base Ugnu Plane Well log colorfill: Left: Vshale < 50% Right: Porosity > 15%

  43. 3D VSP Seismic Volume with Geologic Marker

  44. Amplitudes on Geologic Marker at Top of Sand A

  45. Amplitudes on Geologic Marker at Top of Sand A

  46. Amplitudes on Geologic Marker at Top of Sand A ?

  47. Introduction, background & objectives • Survey design • Acquisition & processing • Results & interpretation • Conclusions

  48. Conclusions • The Hot Ice 3D VSP utilized several innovative technologies: • circular shotpoint pattern adapted to fresnel zone changes • 80 down-hole receivers at 25 ft. spacing • high-frequency source signal: average dominant frequency of 110-130 Hz

  49. Conclusions • The VSP data correlated very well with log and core data. • VSP interpretation indicated hydrates may be present nearby. • VSP data support the concept that methane hydrates are distributed as “patchy” accumulations. • High-frequency seismic data will be necessary to identify and map hydrate targets.

  50. Acknowledgements • The authors wish to thank Anadarko Petroleum Corp, Maurer Technology, Noble Drilling, P/GSI, PGS Onshore and Geometrics for their valuable input into this project. • We want to thank BP, ConocoPhillips and WesternGeco for permission to show the seismic data from the Hot Ice area. • This project was made possible through a cooperative agreement with the U.S. Department of Energy’s Office of Fossil Energy, contract DE-PS26-01NT41331.