The Relationship between Uncertainty and Quality in Seismic Data EXPLORATION SERVICES RESERVOIR SERVICES PRODUCTION MULTI-CLIENT 3D DATA The Relationship between Uncertainty and Quality in Seismic Data by Gregg Parkes and Chris Walker PGS Research

The Relationship between Uncertainty and Quality in Seismic Data Talk Outline The Relationship between Uncertainty and Quality in Seismic Data Introduction Stacking velocity errors Acquisition parameter uncertainty Conclusions

What limits the quality of the seismic image? Geology Acquisition - geometry - parameter variations Processing - underlying processing model - errors - statics, stacking velocity, migration velocity, etc…..

Relating uncertainty to quality Systematic approach : Model acquisition and/or processing uncertainty and determine effect on image at the target

Possible measures of quality : Measuring quality Possible measures of quality : S/N ratio Wavelet coherency Bandwidth AVO attributes Other appropriate signal characteristics In general, selected quality measures will be target specific

The Relationship between Uncertainty and Quality in Seismic Data Talk Outline The Relationship between Uncertainty and Quality in Seismic Data Introduction Stacking velocity errors Acquisition parameter uncertainty Conclusions

Shallow data example

Deep data example

Statistical distribution of picks

Velocity picking errors for shallow dataset

Velocity picking errors for deep dataset

Velocity experiment summary Error distribution is close to Gaussian Depth dependence strong Noise level dependence weak Geology dependence strong 1.5% (s.d.) error is close to theoretical limit Typical data ( < 5 seconds ) 2% - 4 % (s.d.) is representative Deep dataset gave range from 0.5% (shallow) up to 10% -15% (deep/poor quality)

Mapping from velocity uncertainty to quality

The Relationship between Uncertainty and Quality in Seismic Data Talk Outline The Relationship between Uncertainty and Quality in Seismic Data Introduction Stacking velocity errors Acquisition parameter uncertainty Conclusions

How do these allowed variations impact image quality? Typical acquisition specifications - source tolerances Timing :  1 msec Depth :  0.5 m Drop-outs :  10% peak amplitude  10% Primary/Bubble ratio How do these allowed variations impact image quality?

Mapping from timing uncertainty to quality

Timing, depth and drop-out comparison

Random and systematic depth comparisons

Velocity errors - 90% confidence bands

Absolute threshold from statistical analysis of uncertainty

The Relationship between Uncertainty and Quality in Seismic Data Talk Outline The Relationship between Uncertainty and Quality in Seismic Data Introduction Stacking velocity errors Acquisition parameter uncertainty Conclusions

The Relationship between Uncertainty and Quality in Seismic Data Conclusions The Relationship between Uncertainty and Quality in Seismic Data Uncertainty in both acquisition and processing parameters produce changes in seismic quality Quality effects can be balanced against each other to set equivalent tolerances Analysis of uncertainty must be target specific, including choice of quality attributes