Depth Imaging: Todays Tool for Risk Reduction Todays Tool for Risk Reduction

Highlights Depth imagingDepth imaging –Reasonable timeframe –Reasonable cost –Superior images –Simpler, more geologic –Reduced exploration risk

Overview Differences: Time and depth migrationDifferences: Time and depth migration PSDM: Tiered approach to depth imagingPSDM: Tiered approach to depth imaging Resource play data exampleResource play data example Tiered Depth-imaging summaryTiered Depth-imaging summary

Differences: Time & Depth Migration Algorithms are fundamentally the sameAlgorithms are fundamentally the same –Traveltime surfaces are the difference Time migration:Time migration: –2D ray tracing from image point Depth migration:Depth migration: –3D ray tracing from acquisition geometry

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

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

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

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

Tier 3: Anisotropic PSDMTier 3: Anisotropic PSDM –Epsilon (moveout complexity) scans for given Delta –Continue to reduce risk… PSDM: Tiered depth imaging

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

US Land Resource Play Example

Prestack Time PreStack Time Migration Image

Prestack Time PreStack Time Migration Image

Tier 1 Prestack Depth PreStack Depth Migration Image

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

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

Move to Tier 2 Tier 2 Iterative Tomography: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 10The X, Y, Z improvement in resolution compared to Tier 1 is approximately a factor of 10 Top-down layer stripping is seldom successfulTop-down layer stripping is seldom successful –Responsible for lengthy PSDM processing times

PSTM PreStack Time Migration Image

Tier 1 PSDM Tier 1 Depth Migration Image

Tier 2 PSDM (tomo) Tier 2 Depth Migration Image

Iteration QC Each iteration of migration should yield a more focused and structurally simpler imageEach iteration of migration should yield a more focused and structurally simpler image –Interpretationally intuitive

Tier-1 Sed Vel PSDM Tier 1 Depth Migration Gathers

Tier-2 Tomography Tier 2 Depth Migration Gathers

Tier 2 Summary A gridded, tomographic update yields greater resolution and image quality than PSTM or Tier 1 PSDMA gridded, tomographic update yields greater resolution and image quality than PSTM or Tier 1 PSDM An important risk-reduction to evaluate the Tier 1 productAn important risk-reduction to evaluate the Tier 1 product

Tiered Depth Imaging Summary Leverage PSTM effort and workflowLeverage PSTM effort and workflow Critically evaluate your PSTM imageCritically evaluate your PSTM image Improved image, reduced riskImproved image, reduced risk EconomicEconomic Quick cycle-timeQuick cycle-time Intuitive, interpreter-oriented quality controlIntuitive, interpreter-oriented quality control

Key Points – Again… Depth imagingDepth imaging –Reasonable timeframe –Reasonable cost –Superior images –Simpler, more geologic –Reduced exploration risk

Can you afford not to image in depth?Can you afford not to image in depth?

Presenter Contact Information Russell Kappius Senior Advisor, Geophysics and Development Sterling Seismic Services Ltd Littleton, Colorado (303)