The Checkshot + markers method blends absolute depth-time calibration from checkshot surveys with intermediate depth picks supplied by well markers. Markers anchor velocity where checkshot sampling is sparse; checkshot calibrates absolute times. A kriging-based interpolator combines both sets of constraints into a single interval velocity cube.

Required inputs

• Checkshot data — one or more wells with depth-time tables.
• Markers — picks available on the same or on neighbouring wells.
• Constant Velocity — fallback value applied where neither checkshot nor markers constrain the grid.

Parameters

• Datum, Max Depth, Depth Step — output cube extent and sampling.
• Topography type — Internal or External topography.
• Min / Max Velocity — hard bounds clamping the output cube to physical values.
• Mapping parameters: control the well-tie interpolation.

• Max marker deviation from well — search radius used to associate markers with wells (default 50 m).
• Well Tie Interpolation type — Voronoi / ABOS / Triangulation / Kriging (default Kriging).
• Trend smooth — spatial smoothing radius applied to the trend (default 1000 m).
• Kriging Covariance — Spherical / Gaussian / Exponential, plus Kriging Range (correlation distance).
• Marker type interpolation — Linear or Regression; the regression mode adds a polynomial trend with user-supplied Regression coefficient.
• Extrapolate Checkshot and Extrapolate Checkshot to 0 — extend checkshot-derived velocity below the last layer and up to the surface.
• Max distance to layer — wells further than this distance from the current layer are excluded.

Workflow

1. Select Checkshot + markers in the wizard.
2. Configure Datum, Max Depth, Depth Step, Constant Velocity, Topography, Min/Max Velocity.
3. Open the Mapping parameters section and choose an interpolation type and kriging settings.
4. Enable checkshot extrapolation options if the model must extend beyond the checkshot sampling.
5. Run the model. Interval velocities are computed from checkshot, corrected by markers, and interpolated into the grid.

Output

Interval and average velocity cubes, depth/time maps, per-well tie-quality metrics and mismatch logs at every marker used in the calculation.

When to use

• Wells carrying both checkshot and marker data.
• Areas where markers give lateral control that pure checkshot extrapolation cannot reach.
• When depth-time calibration and structural constraint need to be honoured in the same model.

If time horizons are available as additional constraints, prefer Checkshot + markers + horizons — it uses all three data types together.

See Also

• Setting up the velocity model
• Checkshot extrapolation
• Checkshot + markers + horizons
• Velocity model QC