Domain conversion workflow

Module overview

What will you learn in this module?

In this module you will learn how use the domain conversion module in Helios.

What input data will be required in this module?
  • Migrated seismic gathers in time in .su format
  • Interval velocities in .su format
What output will you have created in this module?
  • No data will be created in this module

Instructions and screenshots

For domain conversion we require seismic data and a velocity model. The input seismic can be either offset or angle gathers in time. The velocity model needs to describe the interval velocities as a function of time. The used velocity model ideally starts at the seismic reference datum, otherwise the velocities will be kept constant above the shallowest velocity data that is contained in the provided model. The user should pay attention to use interval velocities but not RMS velocities for the procedure.

While the interval velocity model ideally starts from the surface, the seismic data can start at arbitrary times. The location that will be used for preview can be changed and specified by in-line/x-line numbering.

The user then needs to specify the horizontal dimension of the loaded seismic data which can be either offset or angle. The output is currently fixed to ray-parameter because this is the domain in which the inversion is performed. More options may be added later.

The ray-parameter of the output seismic can be specified by the minimum and maximum value together with the number of p-values.

When pressing Preview the conversion will be performed for the specified location and the results will be displayed. The seismic displays include the input gather and the converted gather before/after sub-stacking. By default su-stacking is enabled by set to 1 trace per bin which effectively means no stacking. The coloured lines in the input gather represent the offset/angle as a function of time for the specified ray-parameters. These rays are computed by ray-tracing through a horizontal overburden model specified by the velocity profile shown on the left.

The signal to noise ratio may be increased if the number of traces to be stacked is increased. In this case a number of rays will be computed around the specified ray-parameter range and stacked within the coloured bins. #Traces defines how many traces are computed and stacked within each bin. The higher this parameter the higher the stack power but also the less the remaining genuine AVO information in the output will be.

The shown critical p-values for the current location and the full volume are for QC purposes only. The user should exceed these values because otherwise the conversion will fail for post-critical offsets or angles.