Setting up the velocity model

A velocity model describes how seismic velocity varies with position and depth across the survey. g-Space uses it to convert interpreted data between the time and depth domains, to build depth maps and cubes, and to support depth imaging and structural interpretation. This chapter describes how to launch the velocity modeling wizard and summarises the eight model-building methods it offers.

Launching the wizard

Open the Velocity model bar in the ribbon.
Click Create depth velocity. The Create velocity model wizard opens.
On the first page, choose one of the velocity model types listed under Velocity models. A preview image illustrates the selected method.
Fill in the parameters and any layer or tie tables that appear for the chosen method, then run the wizard to build the model.

The new model is added to the depth velocity model set and becomes available for time-to-depth conversion and QC. Existing models can be brought in instead with Import velocity model.

Velocity model methods

The wizard offers the following methods, ordered from the simplest to the most data-intensive:

Constant — applies a single interval velocity to the whole output cube.
Constant layered — assigns a constant velocity to each layer, where layers are bounded by horizons, time maps, constant times or topography.
Markers + horizons — derives interval velocities from well marker-to-horizon ties and interpolates them between wells.
Grid velocity by markers + horizons — uses the same marker-to-horizon ties but writes the result on a bin grid.
Checkshot extrapolation — builds a layered cube from well checkshot surveys and extrapolates it across the grid.
Checkshot + markers — combines checkshot depth-time calibration with well-marker depth control.
Checkshot + markers + horizons — combines checkshots, well markers and time horizons in a single well-tied model.
From Vrms — converts stacking / RMS seismic velocities into an interval velocity cube.