2015 Workplan for “VVAz” Analysis of Prestack Migrated Data AASPI 2015 Workplan for “VVAz” Analysis of Prestack Migrated Data Jie Qi and Kurt J. Marfurt (The University of Oklahoma)

Outline Introduction Methodology Application Conclusion Motivation AASPI Introduction Motivation Challenge Methodology VVAz AVAz Azimuthal crosscorrelation Application Geology background Azimuthal attributes Conclusion

Motivation Azimuthally limited or vector-tile gathers are part of the wide-azimuth processing workflow Can we implement interpretation tools to provide residual AVAz analysis capabilities? If the data were migrated using isotropic velocities, these residuals are a measure of VVAz The application of such a tool would increase vertical resolution and precondition the data for subsequent AVAz analysis

Horizontal Transverse Isotropy (HTI) medium (Left): No HTI anisotropy results in equal travel time paths in all azimuths; (Right): In an HTI anisotropic media with aligned vertical fractures the travel time is azimuth dependent and is not equal in all directions. (Courtesy of Close et. al., 2010)

Shear wave spitting in anisotropic medium Receiver VVAZ is based on azimuthal variations in stacking velocity(VNMO) (Courtesy of Ed Garnero)

Fracture: (Photos courtesy of Brian Cardott) Woodford shale Marcellus Shale A key factor in the optimization of reservoir production High natural fractures – high production Helps to identify sweet spots Anisotropic properties: intensity and orientation Anisotropy analysis: amplitude and velocity Left: fractured Woodford shale in the Arbuckle Mountains of southern oklahoma. Right: this is highly fracture shale from Marcellus. Natural fractures enhance or create permeability in the reservoir. (Photos courtesy of Brian Cardott)

Outline Introduction Methodology Application Conclusion Motivation AASPI Introduction Motivation Challenge Methodology VVAz AVAz Azimuthal crosscorrelation Application Geology background Azimuthal attributes Conclusion

Velocity vs. Azimuth (VVAz) Advantages Easy to generate azimuthally-binned data Computation is fast and simple, providing a level of confidence Requires phase- but not amplitude-preservation Disadvantages Suffers from vertical resolution problems associated with Dix’s equation Amplitude vs. Azimuth (AVAz) Advantages Easy to generate azimuthally-binned data Computation is fast and simple, providing a level of confidence Computations are volumetric within the (properly registered) zone of interest Disadvantages Requires amplitude-preserving processing and migration (AVAz) There are two ways to analyze anisotropy in seismic data. One is velocity vs azimuth; and one is amplitude vs azimuth. VVAz and AVAz are both easy to generate azimuthally-binned data

Velocity variation with angle and azimuth (VVAZ) Vint(φ)=V0+εcos[2(φ- φsym)] If ε is zero, it becomes interval velocity. θ N φ φsym VVAZ is based on azimuthal variations in stacking velocity(VNMO) φsym

Amplitude vs. Azimuth (AVAz) Amplitude vs. Offset (AVO) Amplitude vs. Offset (AVO) 8. Attributes applied to offset- and azimuth-limited volumes R(θ,φ)=A+{Biso }sin2θ R(θ,φ)=A+{Biso }sin2θ Amplitude vs. Azimuth (AVAz) Amplitude vs. Azimuth (AVAz) R(θ,φ)=A+{Biso+Banisocos[2(φ- φsym)]}sin2θ R(θ,φ)=A+{Biso+Banisocos[2(φ- φsym)]}sin2θ θ N φ φsym The equation for amplitude vs. azimuth. Note that if Baniso=0 , we obtain the conventional AVO slope-intercept equations. (After Rueger, 1996). (Rueger, 1996)

Workflows Conventional VVAz: AVAz: Generate long-offset sectors or ’tiles’ at different azimuths φ (unmigrated) At discrete picked horizons, compute VRMS as a function of azimuth, φ Compute interval velocities Vint(φ) using Dix’s equation Fit a sinusoidal curve to Vint(φ) to obtain the magnitude and azimuth of anisotropy AVAz: Generate long-offset sectors or ’tiles’ at different azimuths φ (migrated) Pick discrete upper and lower horizons and generate either flattened or stratal slices throughout the volumetric zone of interest At every time or depth sample, fit a sinusoid to the amplitude as a function of azimuth φ

Residual “VVAz” Workflow Shot gathers Prestack Time migration Azim 1 gathers Azim 8 gathers …… Azim 2 gathers AVAz anisotropy Baniso, ψaniso Migrated gathers Dynamic alignment VVAz Anisotropy Structure oriented filter Dynamic alignment

…… Dynamic alignment Correlate adjacent azimuths Find ∆τ and value of highest correlation coefficient Autocorrelate & crosscorrelate Azim 1 Azim 2 Azim 8 Time ……

Vint(φ)=V0+εcos[2(φ- φsym)] Dynamic alignment Least-squares fit ∆τ to find εaniso and φsym Vint(φ)=V0+εcos[2(φ- φsym)] Azimuth, φ V0+εcos[2(φ- φsym)] ε iso ε aniso φsym V0 V0 + ε V0 - ε Example of ellipse fitting on a single bin and time sample. Vertical axis is intensity and horizontal azimuth. (After Roende et al., 2008). (Modified from Roende et al., 2008)

Dynamic alignment Stretch and squeeze data to provide flattened events εaniso and φsym Isotropic Layer 1 Anisotropic Layer 2 High anisotropy Azimuthal data Dynamic alignment Isotropic Layer 1 Anisotropic Layer 2 Isotropic Layer 1 Anisotropic Layer 2 Aligned data

Outline Introduction Methodology Application Conclusion Motivation AASPI Introduction Motivation Challenge Methodology VVAz AVAz Azimuthal crosscorrelation Application Geology background Azimuthal attributes Conclusion

Stratigraphic Cross Section Ellenburger Marble Falls Stratigraphic cross section of the Fort Worth Basin. In the “Core” area of Wise and Denton Counties to the East, the Barnett Shale is subdivided into Upper and Lower units by the intervening Forestburg Lime. The calcite-rich geomechanically ductile Marble Falls and Viola Limestones from hydraulic fracture barriers. The Viola fracture barrier pinches out to the west, such that the Barnett Shale lies unconformably on top of the more brittle, dolomitic Ellenburger Group. The survey in the following figures is on strike with the area of Young County in this image. (After Pollastro et al., 2009) Unconformity (Modified from Pollastro et al., 2009)

Stacked azimuth sector gathers Anisotropy indicators CMP no. CMP 398 CMP 399 CMP 400 0.5 0.6 Time (s) After such migration, note the six azimuthally limited volumes align at the shallow (probably Caddo Lime) horizon but are misaligned at the deeper Barnett Shale target. (After Roende et al., 2008). 0.7 0.8 Data aligned Data Misaligned (Roende et al., 2008)

Amplitude as a function of azimuth (AVAz) ~3500 ft 0.6 0.8 ~8 ms Time (s) 0.7 stronger weaker Sectors from migration with a single velocity field, note the far field move out that contribute to azimuthal velocity variations of around 6.5 %. (After Roende et al., 2008). (Roende et al., 2008)

AVAz products Intercept, A Isotropic gradient, Biso Time (s) 0.4 1.0 Intercept, A Top Marble Fall Top Ellenburger Isotropic gradient, Biso Time (s) 0.4 1.0 Products of the AVAz workflow. (After Roende et al., 2008). Anisotropic gradient, Baniso Time (s) 0.4 1.0 (Modified from Roende et al., 2008) Low High 1 mile

Outline Introduction Motivation Challenge Methodology VVAz AVAz AASPI Outline Introduction Motivation Challenge Methodology VVAz AVAz Azimuthal crosscorrelation Conclusion

Anticipated Challenges Will there be a clear correlation between AVAz and VVAz? Can the residuals be computed gather by gather, or will layer-stripping become important?

Acknowledgements Marathon Oil Co. for a license to their survey AASPI Marathon Oil Co. for a license to their survey Sponsors of the AASPI consortium for financial support and technical encouragement