Practical Depth Conversion with Petrel

Module 1:  Overview of Depth Conversion

Learning Objectives and Importance:    

• Discuss goals for vertical time-to-depth conversion

Topics:          

• Accuracies for relative structure, well prognoses, volumetric estimates and reservoir models
• Database validation QCs
• Indicators for prestack depth migration (PSDM)

Module 2:  Sources of Velocity

Learning Objectives and Importance:    

• Review sources of velocity information

Topics:          

• Sonic logs, check shots and VSPs
• Seismic (refraction and reflection)
• PSDM Tomography
• Full Waveform Inversion

Module 3:  Defining Velocity Types

Learning Objectives and Importance:    

• Review definitions and characteristics of velocities for Petrel representation

Topics:          

• Types of velocities and Petrel Templates
• Conversion of velocity types (e.g. RMS to Interval)
• Import and conversion of velocity text files
• Creating Petrel seismic velocity cubes from text files

Module 4:  Functional Representation of Velocities

Learning Objectives and Importance:    

• Define velocities fields using vertical functions

Topics:          

• Velocity representation via Time-Depth functions
• Velocity as a function of time, V0+KT, and basic database QCs
• Velocity as a function of depth, V0+K(Z-Z0), from well-tie TDRs
• Petrel Velocity Models with time and depth functions

Module 5:  Gridded Representation of Velocities

Learning Objectives and Importance:    

• Define velocities fields using grids

Topics:          

• Spatial velocity variations (lateral gradients)
• Creating an edited PSTM velocity model in Petrel

Learning Objectives and Importance:    

• Implement well-top calibrated depth conversion using T/Z functions and/or Petrel Velocity Models

Topics:          

• Simple, intuitive depth conversion (no velocity model)
• T/Z Function Lookup Table plus Well Adjustment
• QC methods that define Time Depth Relationships (TDRs)
• Basic Petrel Velocity Models
• V0+KT
• Seismic velocities
• V0+K(Z-Z0) from well TDRs
• Time to Depth QCs

Module 7:  Well and Seismic Data Integration

Learning Objectives and Importance:    

• Understand methods for linking well and seismic information in Petrel

Topics:          

• Sonic and density log editing
• Check shot loading and QC
• Establishing seismic data polarity and phase (the wavelet)
• Creating synthetic seismogram well-tie correlations
• Image volumes (“wiggle trace”)
• Inversion volumes (P Impedance)
• Issues with synthetic ties

Learning Objectives and Importance:   

• Appreciate the need to review and correct the database prior to incorporating well control

Topics:          

• Confirm database settings
• Using basic depth-conversion QCs to encounter data discrepancies
• Conditioning Surfaces for input to Models

Module 9:  Vertical Time-to-Depth Conversion (Advanced)

Learning Objectives and Importance:   

• Explore advanced depth conversion with layer-based Petrel Velocity Models

Topics:          

• Geologic and data-driven modeling considerations
• Multi-layer Petrel Velocity Models
• V0 + KT
• V0 + K(Z-Z0)
• PSTM Velocities
• Pseudo Interval Velocities
• Simple Grid Model with edited sonic logs
• Hybrid Models (combinations of above)
• “Simple” thrust models (forming complex models in Petrel)

Module 10: Petrel Models and Uncertainty Analysis

Learning Objectives and Importance:   

• Implement domain conversion and uncertainty analysis with Petrel Velocity and 3D Models

Topics:          

• Evaluating depth uncertainty
• Mean and standard deviation workflow
• Stochastic velocity modeling
• Hidden-well workflow
• Impact of structural uncertainty on volumetrics in 3D Models

Module 11:  Pitfalls of Vertical Depth Conversion

Learning Objectives and Importance:   

• Understand accuracy of vertical time-to-depth methods and when they fail

Topics:          

• QCs and validity of vertical depth conversion
• Impact of geologic complexity
• Alternatives to vertical depth conversion (depth migration, image rays, and map migration)

Module 12:  Calibration of Depth Migration with Well Tops

Learning Objectives and Importance:   

• Learn approaches for stable integration of depth-domain seismic (PSDM) with well control

Topics:          

• Working in the time domain
• Creating the calibrated time/velocity model (the anisotropic Vz model)
• Database QC
• Conversion of time data (seismic/surfaces/faults) to well-top calibrated depth
• Petrel Z-Z depth calibration (depth stretch only)
• Depth Uncertainty Analysis
• Leveraging depth image attributes: A case history