1. High Resolution Carbonate Reef Interpretation Using Cross Well Data
Thomas Morgan, Ph.D., Schlumberger
Mike Raines*, Whiting Petroleum
*formerly with Sandridge Energy
Presented to the Permian Basin Geophysical Society in Midland, TX, 15 October, 2009.

2. Sites: Focus: Michigan West Texas Gross Structure Internal Structure
Depositional Environments

3. Geological Information
Well Logs
Geophysical Data
Geological Interpretation

4. Michigan Silurian Reef
Single profile
Isolated pinnacle reef
Only one additional well
No surface seismic available
First study area.

5. First study field is on a Silurian barrier reef trend in the NW part of the Michigan L.P..

6. Cross well shooting parameters.

7. Tomographic Velocity Inversion
Picked Direct Arrivals
3D Thin Layer Model
3D Ray Tracing
Model Interfaces and Layer Parameters Described by Chebyshev Polynomials

8. Tomographic velocity inversion result
Tomographic velocity inversion result. Red track is Vp, Green over-lay on Vp is Tomographic Vp.

9. Imaging Kirchhoff Integral Prestack Reflection Imaging Depth
Dip Oriented and Aperture Limited
Ray Trace Travel Times from Tomographic Velocities
Angle Gather Output

10. Processed cross well profile
Processed cross well profile. Green log is Vp, blue is gamma, red is neutron porosity. Note 100 foot horizontal guide lines. Recovered at least 800 Hz after imaging.

11. 30 degrees 45 degrees 70 degrees
Profile display is nearly true 1:1. Incidence angles from 30 to 70 degrees were used during imaging. Upgoing reflections.

12. Interpretation Approach
Profile is in Depth
Exact depth tie at the wells
– no time to depth conversion needed
Resolution at the outcrop level – human scale geology
Geological Interpretation versus Geophysical Interpretation
Geologically guided interp, but still have to pay attention to geop – just at a smaller scale.

13. Composite model of Michigan Basin Pinnacle Reef. From Huh et. al
Composite model of Michigan Basin Pinnacle Reef. From Huh et. al., Depositional Environments of Pinnacle Reefs, Niagara and Salina Groups, Northern Shelf, Michigan Basin.

14. Evaporites Reef Zone Grey Niagaran Burnt Bluff Carbonate
Well log only starting point, three wells and major formation tops. Vp and porosity logs shown.
Burnt Bluff Carbonate

15. Processed profile.

16. Bioherm
Reef development seeded by mound buildup.

17. Organic Reef
Bioherm
Main reef side slopes are on the order of degrees.

18. Organic Reef
Bioherm
Flank ruble deposits and other deposits grade laterally into surrounding deeper water depositional sequences.

19. Organic Reef Bioherm Reef Rubble
Flank ruble deposits and other deposits grade laterally into surrounding deeper water depositional sequences.

20. Supratidal Island
Organic Reef
Bioherm
Sub areal exposure.

21. Organic Reef Bioherm Tidal Flats Supratidal Island
Final tidal flats phase.

22. Repeat of Northern Michigan Silurian reef model with depositional environments for reference to interpretation.

23. West Texas Permian Reef
Multiple profiles
More complicated structure
Better well control
Surface seismic available
Second study area.

24. Right
Middle
West Texas profile loop. We will look at the three profiles label “left”, “middle” and “right” from the direction indicated by the arrow. Can now process with a 3D model and honor gross dip trend.
Left

25. Top of reef interpretation from surface seismic overlain on cross well profiles.

26. Detailed cross well interpretation. Top of reef has been re-interpreted. Internal reef structures have been interpreted.
~ Reef Top
Marker Near OWC

27. Stacked Mounds Inter-Mound CO3 Debris
Shaley Lag Deposit
~ Reef Top (Erosional)
On Lap
Enlargement of left profile. Note how the wells are honored much more closely on the cross well interpretation.
Inter-Mound CO3 Debris
Marker Near OWC

28. Stacked Mounds Inter-Mound CO3 Debris
~ Reef Top
Enlargement of Middle profile.
Inter-Mound CO3 Debris

29. Shaley Lag Deposit
~ Reef Top
Enlargement of right profile.

30. Conclusions Depth profiles provide unambiguous well ties
Resolution allows a truer look at the geology
Geophysical effects pushed down to smaller scale
Reservoir level geologic Interpretation is possible
Second study area.

31. High Resolution Interpretation of a Permian Reef
Michael A. Raines, Sandridge Tertiary, LLC,
Thomas R. Morgan*, Ph.D., Schlumberger
Poster PDC P2, Station D1
Tuesday, October 27 at 11:40 a.m.
Shameless promotion!

32. Acknowledgments:
We would like to thank Sandridge Energy and Michigan Technological University for the use of the data.
References:
Bube, K., and R. Langan, 1999, On a continuation approach to regularization for crosswell tomography: 69th Annual International Meeting, SEG, Expanded Abstracts,
Liao, Q., and G. A. McMechan, 1997, Tomographic imaging of velocity and Q, with application to crosswell seismic data from the Gypsy Pilot Site, Oklahoma: Geophysics, 62,
Quan, Y., and J.M. Harris, 1997, Seismic attenuation tomography using the frequency shift method: Geophysics, 62,
Huh, M.H., L.I. Briggs, and D. Gill, 1977, Depositional Environments of Pinnacle Reefs, Niagaran and Salina Groups, Northern Shelf, Michigan Basin, in: Studies in Geology No. 5, Reefs and Evaporites – Concepts and Depositional Models, AAPG, J.H. Fisher ed.