Our comprehensive multistage full-wave inversion workflow involves dynamic-warping FWI, image-guided FWI, wavepath reflection FWI and high resolution reflection FWI

Full waveform inversion (FWI) develops a subsurface model that best explains the observed seismic data through iteratively minimizing the misfit between modelled and observed data.

This is inherently a nonlinear optimization problem and thus often suffers from local-minima and cycle-skipping issues. To attack these issues, TGS FWI uses a dynamic warping technique to resolve long wavelength components; then image-guided FWI starts from low frequency, small offset data, and gradually extends to higher frequency and longer offset data for shallow model inversion. Diving-wave FWI can also be used to update anisotropy parameters. The process then turns to reflection mode; get large wavenumber background update through the wavepath kernel, and then changes to phase-only reflection FWI for high-resolution model update. TGS FWI provides a spatial correlation map, phase residual map and other tools to QC the convergence and possible cycle skipping. TGS FWI can handle all types of acquisitions (NAZ/WAZ streamer, OBC/OBN, land etc.) and provide a high-resolution model for imaging uplift.

Jian Mao , James Sheng , Matt Hart , and Taejong Kim (2016) ”High-resolution model building with multistage full-waveform inversion for narrow-azimuth acquisition data.” The Leading Edge, 35(12), 1031–1036.

A. Salem, M. Hart, S. Baldock, C. Lang, J. Chen, J. Sheng; 2018, “Image Guided Full Waveform Inversion (IGFWI) Modelling of Shallow Channel Features in the Moray Firth”, EAGE

 

Capreolus 3D

  • Offshore NW Australia NAZ
  • Streamer length: 8000 m
  • Water bottom: 100-200 m

 

Challenges:

  • Shallow water
  • Cycle skipping
  • Multiples

 

FWI approach:

  • Dynamic warping FWI
  • Diving wave FWI
  • Reflection FWI
Capreolus Map 716X494

 

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Capreolus 3D: Seismic Before
Capreolus Stk B4 650X495-1
Capreolus 3D: Seismic After
Capreolus Stk after 650X495

 

Capreolus 3D: Velocity

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Capreolus 3D: Velocity Before
Capreolus Depth Slice B4 650X495 (1)
Capreolus 3D: Velocity After
Capreolus Depth Slice after 650X495

 

 

Alonso 3D

  • Offshore Gulf of Mexico NAZ
  • Acquisition: flip-flop
  • Streamer length: 10100 m x 10 cables
  • Water bottom: 1888-3025 m
  • Size: 6269 km2

Challenges:

  • Deep water
  • Minimal diving wave data

FWI approach:

  • Reflection FWI due to lack of diving waves
Alonso Map 613X482

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Alonso 3D: Stack Before
Alonso Stk B4 650X495
Alonso 3D: Stack After
Alonso Stk after 650X495

 

Alonso 3D: Depth

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Alonso 3D: Depth Before
Alonso Depth Slice B4 650X495 (1)
Alonso 3D: Depth After
Alonso Depth Slice after 650X495

 

Crean 3D

  • Porcupine Basin, Celtic Sea NAZ
  • 5400 km2 new, 1000 km2 legacy acquisition
  • Streamer length: 8000 m
  • Water bottom: 450-2000 m

Challenges:

  • Shallow high-velocity channels
  • Shallow low-velocity gas pockets

FWI approach:

  • Multistage, interleaved with Image-guided Tomography
  • Early iterations: diving wave, dynamic warping FWI
  • Late iterations: phase-only reflection FWI

 

Crean Map 549X475

 

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Crean 3D: Stack Before
Crean Stk B4 650X495
Crean 3D: Stack After
Crean Stk after 650X495

 

Crean 3D: Depth

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Crean 3D: Depth Before
Crean Depth Slice B4 650X495 (1)
Crean 3D: Depth After
Crean Depth Slice after 650X495

 

Ogo 3D

  • Gulf of Mexico OBN
  • 24 km maximum inline offset
  • 8 km maximum crossline offset
  • Source spacing 50 m x 100 m, blended dual sources
  • Good signal down to 2.5 Hz
  • Water bottom: ~500 m
  • Sparse node test: 1x1 km node spacing

Ogo Map 462X505

 

Ogo 3D: Inline Stack

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Ogo 3D: Inline Stack Before
Ogo Inline Stk B4 650X495
Ogo 3D: Inline Stack After
Ogo Inline Stk after 650X495

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Ogo 3D: Crossline Stack Before
Ogo Crossline Stk B4 650X495
Ogo 3D: Crossline Stack After
Ogo Crossline Stk after 650X495
dmh-stack

Dynamic Matching FWI

A step-change in velocity modelling and subsurface imaging results

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