Velocity Analysis
At Spectrum, velocities are picked interactively from gathers, stacks (constant or variable function) and semblance plots. Interpreted horizons can be overlaid the velocity analyses to allow horizon consistent velocity picking.
The velocities are checked interactively with NMO corrected gathers, stacks and iso-velocity plots. A regional Q.C. of all velocities is made and maps can be produced for velocity at given times or times at given velocity.
For 3D datasets, a velocity cube is created and iso-velocity plots are produced for inlines, cross lines and constant time slices. Iso-velocity plots can also be produced for interpreted horizons and as 3-dimensional contour maps.
An optional fourth order NMO term is available which compensates for ray bending at far offsets. Following the initial velocity pick a contour plot of the C4 term is produced and also picked interactively as shown below.
The module VELTUNE is Spectrum’s proprietary automatic continuous velocity analysis package. The program produces velocity information for each sample of each mid-point bin. Mid-point gathers, plus a preliminary picked velocity field e.g. on a 1 km grid are input to VELTUNE and an analysis of the residual velocities is made. These velocity corrections are derived from maximum energy calculations along moveout curves for each sample on each gather.
VELTUNE has options to derive residual NMO corrections plus optionally either C2 (4th order) or Eta corrections. The raw velocity picks can be filtered to give a final velocity cube.
