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.

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

Geological Information Well Logs Geophysical Data Geological Interpretation

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

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

Cross well shooting parameters.

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

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

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

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.

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.

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.

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.

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

Processed profile.

Bioherm Reef development seeded by mound buildup.

Organic Reef Bioherm Main reef side slopes are on the order of 30-45 degrees.

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

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

Supratidal Island Organic Reef Bioherm Sub areal exposure.

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

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

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

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

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

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

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

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

Shaley Lag Deposit ~ Reef Top Enlargement of right profile.

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.

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!

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, 1295-1298. 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, 1804-1811. Quan, Y., and J.M. Harris, 1997, Seismic attenuation tomography using the frequency shift method: Geophysics, 62, 895-905. 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.