Simple velocity tie (to wells)

Creating velocity volumes is easy in Insight - just take a look at some of our suggested workflows.

Matching a velocity to tie the well location can be more troublesome. A simple velocity tie can be achieved by calculating the vertical interval velocity in time (V0) from any "isotropic interval velocity model" in time, possibly from depth migration or velocity picking, and an interval delta model in time. Insight packages this workflow up into easy-to-use processes available in the Explorationist and Image Gather Processing modules.

The workflow can be split into 3 stages:

  1. Use the Synthetics tool to create delta curves for each well that you want to influence the model.
  2. Create an interval delta model in time.
  3. Calculate V0 from delta and isotropic depth mig velocities.

1. Synthetics tool delta curves

Generate the delta curve for the wells in DUG-Insight’s Synthetics tool. The delta curves will then be used to build 3D delta models (see Delta Model).

  1. As a prerequisite, you need to load the (NMO) interval velocity volume and select it for time/depth conversion as described in Converting Time-Depth

Note: The delta curve is calculated at the wells using the well’s checkshot Vint and an initial (NMO) isotropic Vint field selected for Time-Depth Conversion (See Generate Delta Curve).

  1. In the Synthetics window, open the View tab.
  2. Under the Tracks section, click the amber circle at Delta to display the Delta track in Synthetics.
  1. Open the Delta tab in the Synthetics window.
  2. Select the Calculate Delta check box. This is to create the delta curve.
    • Note: Delta values are required to be in the range of -0.25 to 0.35.
  3. At NMO Velocity, the velocity volume selected for time/depth conversion is shown.
  4. At Extrapolation Top, select Well Water Bottom or Horizon (and select the water bottom horizon). This parameter defines the depth above which the delta value will be extrapolated.
  5. Type the display sample interval for the delta curve at Display Sample Interval (m). By default, this is set to "20".
  6. At Smoothing Window (m), type the smoothing value for the delta curve. By default, this is set to "12".
  7. Select the blocking option to be used for the delta curve after smoothing at Blocking.
    • No Blocking: Display the smoothed delta based on the display sample interval.
    • Regular Blocking: Use the regular blocking option and type the block size in meters for the delta curve (this is equivalent to making a coarse sample interval).
    • Horizon Blocking: Use the horizon blocking option and select the horizon(s) used in the blocking. To add the horizons, click the Add Row icon.
  8. QC the delta curve generated. Valid delta curve results must be in the range from -0.25 to 0.35.

2. Create an interval delta model in time.

The Delta Model process builds a delta model from well curves. It requires a windowing model (see Creating a Windowing Model) and at least one well with a delta curve. 

Window model layers are automatically divided by ghost horizons using the conformability specified in the windowing model. Delta values are selected for the model at the intersection between each well and the ghost layer. These values are combined according to the specified per-layer settings.

Note: Create the Window model in Time as Delta model process creates an interval delta model in time.

  1. In the Control Panel, open the Process tab.
  2. At the tab header, click the blue "+" icon and select New Process.
  3. Double-click Delta Model.
  4. Type a name for the process and click OK.
  1. Select the windowing model to be used in the process at Layer horizons - select a windowing model (see Creating a Windowing Model).
  2. In the Output Extents section, select a survey to be used in the delta modeling process at Survey.
  3. Type the range of Inline extent, Crossline extent and time (TWT) extent for the delta model and the respective sample intervals.
  4. In the Wells section, click the Add Row (blue "+") icon to add the wells used in the delta modeling.
    Note: Specific vertical extents can be specified at each well by selecting  Specify well curve vertical extents (ms) option.
  5. Select the delta curve for each well to be used in the delta modeling. 
  6. In the Per-Layer Settings section, select the calculation type used to distribute delta in each layer in the windowing model. Available options include:
    • Inverse Distance
    • Average of Well Values
    • User-specified constant
  7. As a result of this process, a new delta volume is added in the Volume tab. You can further smooth the delta model using the Volume Smoothing process.

3. Calculate V0 from delta and isotropic depth mig velocities.

Calculates the vertical interval velocity in time (V0) from an isotropic interval velocity model in time, and an interval delta model in time.

  1. In the Control Panel, open the Process tab.
  2. At the tab header, click the blue "+" icon and select New Process.
  3. Double-click V0 from delta and isotropic depth mig velocities.
  4. Type a name for the process and click OK.
  1. Select the nmo interval velocity volume (in time) used in delta calculation.
  2. Select the delta model (time).
    • Volume is calculated using formula Vo/Vnmo = 1/sqrt(1+2*delta)
    • See paper Tsvankin, I., 2012, Seismic signatures and analysis of reflection data in anisotropic media: Society of Exploration Geophysicists, third edition.  
  3. As a result of this process, a new volume that ties the well locations is added in the Volume tab. You can further smooth the delta model using the Volume Smoothing process.