Demultiple Routes


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Different Seismic Demultiple Approaches applied in GLOBE Claritas

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Demultiple Routes

  1. 1. GLOBE Claritas™Demultiple Approaches
  2. 2. Primary Demultiple Approaches• Deconvolution – multiple considered as reverberation – Tau-P, shot and receiver location ensemble etc.• RADON demultiple (PRT_DEMULT) – Velocity discrimination (parabolic approximation) – Use primary or multiple model (reject down or flat dips) – High resolution mode via Harlan transform• Flattening on Offset Planes – Digitise seafloor (and/or peg-leg generator) – Flatten multiple via static shits and remove flat events• SRME and subtraction – Two good subtraction routines (MONK/WANG) – Limitations on long offset and deep water – Flatten multiple via static shits and remove flat events
  3. 3. RADON Anti-Multiple : theory Primary Multiple 300ms far offset moveout, measured via ruler (RMB click) • Data summed along parabolas • Defined by far offset moveout (FOM) in ms • This example : 90% NMO applied • Multiples +ve P-values • Primaries -ve P-Values • Data outside of the Radon transform range is retained • Define a modelled range (in FOM) and a noise range to remove • “Cross” shape in Radon-space focussed to a point by Harlan mode
  4. 4. PRT_DEMULT Example : Input data 700ms FOM used
  5. 5. PRT_DEMULT Example : Harlan Demultiple
  6. 6. Flattening on Offset Planes ExampleStrong shallow multiple Digitise multiple Apply an FK filter Remove all shiftsWater-velocity FK Shift data down by 1000ms Reject +/- 0.5ms per trace applied Shift data up by multiple time Applied from 950-1050ms Multiple flat at 1000ms• Only effective where multiple crosses primaries• Can apply again for the second bounce• Can apply pre-stack – use FLATTEN on offset planes
  7. 7. SRME Example • Model created by cross correlating shot and receiver gathers (SRME)Original Shot Modelled multiple Subtracted result • Data needs to be extended to zero offset (OFFREG) • Shot and receiver spacing needs to be the same (OFFREG, SHOTINT) • Should not process incoming data at all – except perhaps mute and filter • Only models reflections, not refractions • Theoretically needs full fold shot and receiver gathers to be most effective • In deep water, limiting the shot and receiver domain offsets can be beneficial • Use adaptive subtraction to remove the multiple (WANGSUBT, MONKSUBT or combinations of these) • Complex workflow, consider simple multiple modelling (MULMOD)
  8. 8. Basic Processing Routes Re-sampled Shots Tau-P Decon. SRME Radon Hi res Radon Tau-P Decon. Offset Offset Offset Plane Plane PlaneStack #1 Stack #2 Stack #3 Stack #4 Stack #5 Stack #6 Stack #7 Stack #8No demultiple used RADON approaches SRME approaches
  9. 9. #1 Stack : No Demultiple
  10. 10. #2 Stack :Tau-P Decon.
  11. 11. #3 Stack : Tau-P Decon, Radon
  12. 12. #4 Stack : Tau-P Decon, Radon, Offset
  13. 13. #5 Stack : Tau-P Decon, Radon/Harlan
  14. 14. #6 Stack : Tau-P Decon, Radon/Harlan, Offset
  15. 15. #7 Stack : SRME, Tau-P Decon
  16. 16. #8 Stack : SRME, Tau-P Decon, Offset
  17. 17. Examples on line TL-01• Raw data has 50m SP, 25m groups, 120 channels• Minimum Offset is 189.4m• Tau-P run with 50m SP, 6.25m groups• SRME run at 25m SP, 25m groups• Stacks etc. created with 12.5m SP, 25m groups• All managed via OFFREG and SHOTINT• Spike QC important pre-interpolation
  18. 18. Radon Parameters Used• Offsets 184.9m to 3159.9m increment 25m• Fold 120, HMAX 3159.9• Model MS: -700 to 700• Noise MS: 60 to 696• 300 p-values (3Hz-80Hz range)• Start time 1.75x water bottom, 200ms minimum
  19. 19. Offset Plane Parameters Used• Digitised Seafloor on near trace plot• DSORTOFF to sort to common offset planes• FLATTEN to flatten 1st multiple• QFKPS FK filter +/-50ms around flattened multiple• Filter set to reject flat data, 150 trace window• Repeat for the 2nd multiple• Sort back to CDP order via DISCGATH
  20. 20. SRME Parameters Used• Three passes of adaptive subtraction• WANGSUBT with 80% eigen values• MONKSUBT 300ms gated• MONKSUBT 100ms gated• Run using REREAD and pseudo traces