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<< Click to Display Table of Contents >> Navigation: Best Practice Flows > Velocity model workflow > Setting up the velocity model > Checkshot + markers + horizons |
The Checkshot + markers + horizons method is the most comprehensive velocity-building tool in g-Space. It combines three data types: checkshot surveys for absolute depth-time calibration, well markers for lateral velocity variations, and time horizons for structural framework. All three are fed into a single kriging-based solver that produces a layered, well-tied interval velocity cube.
•Checkshot data — on one or more wells.
•Markers — picks on wells, typically one per stratigraphic unit.
•Time horizons — bounding surfaces for the layers.
•Marker-to-horizon tie table — each row links a time horizon to a marker or marker group. A Trend column controls how velocity is guided laterally: None, Vrms, Layer width, or Data map, with optional inverse trend and Use markers inside group only flags.
•Datum, Max Depth, Depth Step, Bottom Velocity, Constant Velocity — output extent and fallback velocities.
•Topography type, Min / Max Velocity — same role as in Checkshot + markers.
•Min thickness for velocity calculation — skip layers thinner than this threshold.
•Compute mismatch for all wells — produce tie-quality logs for every well, not only the ones used in calibration.
•Mapping parameters: same interpolation controls as in Checkshot + markers (Max marker deviation, Well Tie Interpolation type, Trend smooth, Kriging Covariance and Range, Marker type interpolation, Regression coefficient, Extrapolate Checkshot, Max distance to layer, Use wells and horizons inside polygon).
•Calculate velocity by checkshots — if enabled, velocity is derived directly from the checkshot curve; otherwise the marker-based formulation is used.
•Add marker horizons — create interpreted horizons at marker depths and include them in the output.
•Use marker projection if marker not exists — project nearby marker picks when the marker is missing at a well.
•VrmsStep — sampling step for Vrms-based trend constraints.
1.Select Checkshot + markers + horizons in the wizard.
2.Configure cube extent (Datum, Max Depth, Depth Step, Bottom / Constant Velocity), topography and velocity bounds.
3.Populate the marker-to-horizon tie table. For each row choose a horizon, a marker and optionally a trend.
4.Configure the Mapping parameters (interpolation, kriging, marker smoothing).
5.Decide whether velocity should be driven by checkshots or markers via Calculate velocity by checkshots.
6.Enable QC and projection options as required and run the model.
Layered interval velocity and average velocity cubes tied to the time horizons, depth and time maps, optional marker horizons, per-well time-depth mismatch logs and pine charts for quality control.
•Mature fields where all three data types are available.
•Production velocity models used for time-to-depth conversion and reserves estimation.
•Projects requiring rigorous QC via per-well mismatch logs and marker-horizon consistency.
If any of the three data types is missing, choose the method that uses only the available combination (for example Checkshot + markers or Markers + horizons).