Depth Imaging:

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• Depth Imaging
• Todays Tool for Risk Reduction

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Highlights

• Depth imaging
• Reasonable timeframe
• Reasonable cost
• Superior images
• Simpler, more geologic
• Reduced exploration risk

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Overview

• Differences Time and depth migration
• PSDM Tiered approach to depth imaging
• Resource play data example
• Tiered Depth-imaging summary

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Differences Time Depth Migration

• Algorithms are fundamentally the same
• Traveltime surfaces are the difference
• Time migration
• 2D ray tracing from image point
• Depth migration
• 3D ray tracing from acquisition geometry

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Differences Time Depth Migration

• Time migration
• Velocities are less geologic and have low spatial
  resolution
• Lateral velocity variations produce mis-imaging
• Depth migration
• Velocities are more geologic, with higher spatial
  resolution
• Algorithmic accuracy results in better focusing
  and stable phase in the data

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PSDM Tiered depth imaging

• Leverage PSTM velocities
• Global tomographic inversion (not Dix!) to
  generate robust depth/interval-velocity field
• Ensure geologic consistency
• Successive decision points
• Tier 1 Initial depth volume
• Geologically simpler
• Tier 2 Iterative tomographic updates of
  velocities
• Establish survey-resolution velocity limits
• Tier 3 Vertical well-log registration
• Define anisotropic parameters for advanced imaging

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PSDM Tiered depth imaging

• Tier 1 Initial depth volume and gathers
• Decision Point
• Validate PSTM volume?
• Interpretation proceeds
• Significant differences?
• Prioritize to Tier 2
• or
• Prioritize for internal company depth imaging

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PSDM Tiered depth imaging

• Tier 2 Iterative tomographic refinement of
  velocities
• Gathers well behaved?
• Establish survey-resolution velocity limits
• Vertical well-log registration
• Significant Delta (seismic/well depth
  differences)?
• Move to Tier 3
• Establishing need for Tier 3 reduces risk

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PSDM Tiered depth imaging

• Tier 3 Anisotropic PSDM
• Epsilon (moveout complexity) scans for given
  Delta
• Continue to reduce risk

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Depth Migration Value

• Continued refinement of seismic data
• Well-defined flow with intuitive decision points
• Natural progression from time-to-depth imaging
• Use simple, robust tomographic solution (Tier 1)
• Extract information already contained in seismic
  volumes
• Not restricted to complex geology (Tier 2)

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US Land Resource Play Example
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Prestack Time
PreStack Time Migration Image
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Prestack Time
PreStack Time Migration Image
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Tier 1 Prestack Depth
PreStack Depth Migration Image
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Tier 1 Summary

• Superior imaging to PSTM
• Leverages PSTM velocities
• Necessary step prior to Tier 2
• Tier 1 residuals are quantitative indicator for
  Tier 2
• A critical risk-reduction tool for evaluating
  PSTM

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Tier-1 PSDM Gathers
Tier-1 Depth Migration Gathers
Note moveout not addressed by Tier 1 product QC
for Tier 2
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Move to Tier 2

• Tier 2 Iterative Tomography
• Yields greater velocity resolution and a refined
  depth image
• What spatial resolution can we expect from Tier 2
  Depth migration velocities?
• The X, Y, Z improvement in resolution compared to
  Tier 1 is approximately a factor of 10
• Top-down layer stripping is seldom successful
• Responsible for lengthy PSDM processing times

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PSTM
PreStack Time Migration Image
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Tier 1 PSDM
Tier 1 Depth Migration Image
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Tier 2 PSDM (tomo)
Tier 2 Depth Migration Image
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Iteration QC

• Each iteration of migration should yield a more
  focused and structurally simpler image
• Interpretationally intuitive

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Tier-1 Sed Vel PSDM
Tier 1 Depth Migration Gathers
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Tier-2 Tomography
Tier 2 Depth Migration Gathers
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Tier 2 Summary

• A gridded, tomographic update yields greater
  resolution and image quality than PSTM or Tier 1
  PSDM
• An important risk-reduction to evaluate the Tier
  1 product

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Tiered Depth Imaging Summary

• Leverage PSTM effort and workflow
• Critically evaluate your PSTM image
• Improved image, reduced risk
• Economic
• Quick cycle-time
• Intuitive, interpreter-oriented quality control

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Key Points Again

• Depth imaging
• Reasonable timeframe
• Reasonable cost
• Superior images
• Simpler, more geologic
• Reduced exploration risk

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• Can you afford not to image in depth?

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Presenter Contact Information Russell
Kappius Senior Advisor, Geophysics and
Development Sterling Seismic Services
Ltd Littleton, Colorado 80120 [phone]