Impact of MD on AVO Inversion Jianhua Yu University of Utah

Outline Motivation Methodology Numerical Tests Conclusions Synthetic data Field marine data Conclusions

Prestack migration based AVO Inversion Prestack migration to generate the common offset data, CRGs, and angle gathers AVO analysis or inversion (Shuey, 1985)

What Influences the Accuracy of AVO? Preprocessing such as amplitude balance, demultiple etc. Migration noise, footprint due to coarse acquisition

Migration Problem Seismic Trace Migration Ellipse Layer 1 Layer 2 Incorrect Contribution Layer 1 Layer 2 Actual reflection point

Migration Deconvolution Reduce prestack migration noise and artifacts Improve prestack migration image

Motivation Develop a MD-AVO method Reduce migration artifacts Improve data for AVO analysis and seismic attribute analysis

Outline Motivation Methodology Numerical Tests Conclusions Synthetic data Field marine data Conclusions

Migration Section = Blurred Image of true reflectivity model m Migration Deconvolution m’ = L d T L m but d = L m Migrated Section Migration Section = Blurred Image of true reflectivity model m Data

How to Get the True Reflectivity Model m Deconvolve the point scatterer response from the migration image T m = (L L ) m’ -1 Reflectivity Migrated Section Deblurring filter

How MD conjunct with AVO Data in common offset domain satisfies the local property of MD filter Common offset section is natural domain for AVO analysis

Processing Steps: Preprocessing : Geometric spreading correction, amplitude balancing, and demultiple Velocity analysis and estimate RMS velocity model for migration in time domain Prestack migration/inversion to generate the migrated COG and angle gathers

MD-AVO Methodology Apply MD to common offset sections Normal AVO parameter inversion Apply MD to AVO section

Outline Motivation Methodology Numerical Tests Conclusions Synthetic data Field marine data Conclusions

Outline Motivation Methodology Numerical Tests Conclusions Synthetic data Field marine data Conclusions

Prestack Migrated COG (45-55) Section X(km) X(km) 1 5 1 5 2.5 2.5 CDP 150 Time (s) Mig Mig + MD

Closeup of COG (45-55) Section X(km) X(km) 1 2 1 2 0.5 2.5 0.5 2.5 CDP 150 Time (s) Mig Mig+ MD

Spectrums of Mig and MD Images Trace No. Trace No. 100 110 100 110 0.0 60 0.0 60 CDP 150 Frequency (Hz) Mig Mig + MD

Close-up of One CRG Mig Mig + MD X(km) X(km) 1 1.8 1 1.8 0.6 1.8 0.6 Time (s) Mig Mig + MD

Outline Motivation Methodology Numerical Tests Conclusions Synthetic data Field marine data Conclusions

Time (s) Offset (km) Velocity (km/s) 0.26 2.0 1.5 3.5 1.0 3.0 1.0 3.0 CDP 150 CDP 150 Time (s)

RMS Amp. before and after preprocessing Shot Number 200 800 -6.0 1.442 Offset (km) -3.5 Raw data -6.0 0.322 -3.5 After preprocessed RMS Amp. before and after preprocessing

m = (L L ) L d Get ghosts: Dg=Lmg Primary: dp=d-dg Least Squares Inversion for Demultiples (Taner et al. 1969; Lumely et al., 1998; Zhao, 1996) m = (L L ) L d T -1 Velocity model Hyperbolic operator Seismic data Transpose of L Get ghosts: Dg=Lmg Primary: dp=d-dg

Time (s) Offset (km) Offset (km) Offset (km) Raw data Demultiple 0.26 2.0 Offset (km) 0.26 2.0 Offset (km) 0.26 2.0 Offset (km) 0.0 3.0 CDP1300 CDP1300 CDP1300 Time (s) Raw data Demultiple Multiples

Time (s) Offset (km) Offset (km) NMO raw data NMO demultiple 0.26 2.0 0.0 3.0 0.0 3.0 CDP 1300 CDP 1300 Time (s) NMO raw data NMO demultiple

Time (s) Velocity (km/s) Velocity (km/s) Raw data Demultiple 1.5 3.5 0.0 3.0 0.0 3.0 CDP 1300 CDP 1300 Time (s) Raw data Demultiple

Time (s) Offset (km) Offset (km) NMO raw data NMO demultiple 0.26 2.0 0.0 3.0 0.0 3.0 CDP 1764 CDP 1764 Time (s) AVO ? 2.1 NMO raw data NMO demultiple

RMS Velocity Model X (km) 21 3.5 Time (s) 1.5 m/s 5.0

Comparison of Estimated RMS Velocity and Well Sonic Data Time (s) 3 5 Well Vrms Well Vint Velocity (km/s) Estimated Vrms 1

Stacked Section X (km) 20 7 WELL Time (s) 3.5

Migration Section X (km) 20 7 Time (s) 3.5

MD Result X (km) 20 7 Time (s) 3.5

Comparison of Mig and MD X (km) X (km) 12 18 12 18 Mig Mig+MD Reservoir Reservoir Time (s) 3.5

* P S AVO Parameter : Before MD Reservoir Reservoir After MD X (km) 12.1 X (km) 13.6 1.98 Before MD Reservoir - -3.6 - +2.3 2.20 Time (s) 1.98 Reservoir After MD 2.20

HCI Section Before and After MD X (km) X (km) 18 7 18 7 1.6 Reservoir Time (s) 2.7 Before MD After MD

Outline Motivation Methodology Numerical Tests Conclusions Synthetic data Field marine data Conclusions

Conclusions Improves stratigraphic resolution Attenuates migration noise and artifacts Helps to identify lithology anomaly in AVO section

Future Work Blind Test on More Real Data (We look forward to the donation of data from sponsors) Develop 3-D Prestack MD for Field Data Processing

Acknowledgment Thank 2001 UTAM sponsors for the financial support