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<< Click to Display Table of Contents >> Navigation: Best Practice Flows > Velocity model workflow > Setting up the velocity model > Grid velocity by markers + horizons |
The Grid velocity by markers + horizons method uses the same marker-horizon ties as the Markers + horizons method but outputs the velocity cube on a user-defined regular XY grid or inside a selected 3D seismic geometry, rather than on the native trace grid of the horizons. Use it when downstream tools need a regular, grid-aligned velocity volume.
•Datum — elevation reference.
•Marker-to-horizon tie table — time horizon + marker/group pairs; same structure as in Markers + horizons.
•Reference Geometry — controls the XY extent and sampling of the output cube. Choose Maps intersection (use the common area of the input maps), Polygon (restrict to a selected polygon) or Seismic 3D (use the bin grid of a selected 3D cube).
•Max Depth — lower bound of the cube (default 4000 m).
•Depth Step — vertical sampling (default 10 m).
•Bottom Velocity — extrapolation velocity below the deepest tie (default 5000 m/s).
•XY Step — horizontal sampling of the output grid (default 100 m). Used when the reference geometry is Maps intersection or Polygon.
•IL Each / XL Each — subsampling factors for the selected 3D cube (default 1). Used when the reference geometry is Seismic 3D.
1.Select Grid velocity by markers + horizons in the Setting up the velocity model wizard.
2.Choose a Reference Geometry (Maps intersection, Polygon, or Seismic 3D) and configure the corresponding XY or IL/XL parameters.
3.Set Datum, Max Depth, Depth Step, Bottom Velocity.
4.Populate the marker-to-horizon tie table.
5.Run the model. Velocities are computed at the ties and interpolated onto the chosen grid.
Interval and average velocity cubes sampled on the regular grid defined by the reference geometry, plus depth and time maps. The lateral node spacing matches either XY Step or the bin grid of the selected seismic cube, depending on the geometry choice.
•When downstream tools (3D-grid creation, reservoir modelling) require a regular, bin-aligned velocity cube.
•When the project area is defined by a bounding polygon and the model must not spill outside it.
•When aligning the velocity cube to an existing 3D seismic volume is important.
For models tied to the native horizon trace grid, use Markers + horizons instead.
•Setting up the velocity model