Description

R-cre to Vrms converts a Common Reflection Element (CRE) velocity model — expressed in terms of the CRE radius parameter R — into a conventional root-mean-square (Vrms) velocity field. The conversion is performed by inverting the CRE moveout equation for Vrms at each time-trace grid point, using a least-squares approach controlled by a regularisation inversion factor. The resulting Vrms volume can be used directly as input to NMO correction, stacking, or depth conversion modules.

This module is typically placed after a CRE velocity analysis module in workflows that use the CRE operator for velocity picking, when the downstream processing chain requires a standard Vrms representation rather than the CRE R-parameter format.

Input data

Input CRE

The CRE velocity model gather (R-parameter field) to be converted. Connect from the output of a CRE-based velocity analysis module.

Velocity picking params

Velocity picking parameter set defining the output Vrms grid geometry (time axis sampling, trace spacing). Connect the same velocity picking params item used in the upstream velocity analysis module.

Parameters

V0

Near-surface reference velocity (m/s) used as the initial velocity at time zero in the CRE-to-Vrms inversion. Default: 1500 m/s. Set this to match the average velocity of the near-surface layer, typically from uphole or refraction data.

Minimum velocity

Lower bound (m/s) on the output Vrms field. Default: 1500 m/s. Vrms values computed below this threshold are clipped to the minimum. Set to a physically plausible water or near-surface velocity to prevent unphysical low-velocity artefacts.

Maximum velocity

Upper bound (m/s) on the output Vrms field. Default: 5000 m/s. Vrms values above this threshold are clipped. Set to a value representative of the maximum expected formation velocity in your survey area.

Minimum time

Start of the time range (s) over which the CRE-to-Vrms conversion is performed. Default: 0.1 s. Set to the shallowest time of interest in the survey.

Maximum time

End of the time range (s) for the conversion. Default: 5 s. Set to the maximum two-way time of interest.

Threshold radius

Minimum CRE radius value (m) below which the conversion is considered unreliable and the output is set to the background velocity. Default: 60 m. Increase this threshold on data where the CRE picking is noisy or the reflector curvature is poorly constrained.

Inversion factor

Regularisation weight (0–1) for the least-squares inversion used to convert R to Vrms. Default: 0.99. Values close to 1 produce a smooth, well-conditioned output closely following the background velocity trend; lower values give a solution more tightly fitting the CRE picks but potentially noisier.

Find step trace grid

Trace decimation step used when searching for the nearest CRE data point during the conversion. Default: 1 trace (no decimation). Increase to speed up processing when the CRE velocity field is densely sampled and the search can safely be coarsened.

Settings

Execute on { CPU, GPU }

Selects the processing device. CPU is adequate for this conversion module.

Distributed execution

Configuration for distributed (cluster) execution.

Bulk size

Minimum number of gathers sent per work chunk during distributed execution.

Limit number of threads on nodes

When enabled, restricts CPU thread count per cluster node to the value in Number of threads.

Job suffix

Optional text appended to the distributed job name.

Set custom affinity

When enabled, applies the CPU affinity mask specified in Affinity.

Affinity

CPU affinity mask applied when Set custom affinity is enabled.

Number of threads

Maximum number of CPU threads used during execution.

Skip

When enabled, this module is bypassed and data passes through unchanged.

Output data

Output VRMS

The output Vrms velocity field converted from the input CRE R-parameter model. Connect to downstream NMO correction, velocity conversion, or depth migration modules that require a Vrms input.

Information

Graphics

Custom actions