Density Voxel to Velocity Conversion

Use the option Voxel > Utilities > Convert Density to Velocity, (geogxnet.dll(Geosoft.GX.VelocityDensityConversion.DensityVoxelToVelocity;Run)*), to convert a voxel containing rock densities into seismic (P-wave) velocities using one of several published methods. The option is also available in the GM-SYS 3D Modelling extension.

Convert Density Voxel to Velocity dialog options

Input density voxel

Select an existing voxel containing density values to be converted.

Script Parameter: VOXDEN2VEL.INPUT_VOXEL

Density units

Select the density units that the values in the input voxel represent.

Script Parameter: VOXDEN2VEL.DENSITY_UNITS

Output velocity voxel

Select the name of the new or existing voxel that will contain the calculated velocity values.

Script Parameter: VOXDEN2VEL.OUTPUT_VOXEL

Velocity units

Select the velocity units that the values in the output voxel represent.

Script Parameter: VOXDEN2VEL.VELOCITY_UNITS

Method

Select the conversion method from the list. The valid range of velocities for each method is shown.

Script Parameter: VOXDEN2VEL.METHOD

Dummy outside range

Each conversion method is defined within a range of velocities (and corresponding densities). Check this box if you wish to dummy calculated values that fall outside of the defined range.

Script Parameter: VOXDEN2VEL.USE_DUMMIES

Application Notes

Published empirical relationships between seismic velocity and bulk density of various rock types are commonly used in processing seismic data (Gardner et al., 1974; Brocher, 2005). The Velocity to Density and Density to Velocity conversions utilize 5th order polynomial expansions to approximate several of these relationships to less than 0.001 g/cm3 variance. Velocity to Density function and the inverse Density to Velocity function should match to within 4 significant figures.

Addtional Custom Methods

Additional Velocity-to-Density conversion functions may be added by editing the %USERPROFILE%\Documents\Geosoft\Desktop Applications \csv\vel_density.csv file. The conversion must be represented by a 5th order or lower polynomial, as described in the file header. Coefficients are appropriate for Velocity units of m/s and Density units of g/cm³ and unit conversions are performed by the GXs.

References

  • [1] Gardner, G.H.F., Gardner, L.W., and A.R. Gregory, 1974, "Formation velocity and density - the diagnostic basics for stratigraphic traps", Geophysics, vol. 39, no. 6, pp. 770-780.
  • [2] Brocher, T.M., 2005, "Empirical relations between elastic wave speeds and density", Earth's crust Bulletin of the Seismological Society of America, vol 95, no. 6, pp. 2081-2092.

*The GX.NET tools are embedded in the geogxnet.dll file located in the "...\Geosoft\Desktop Applications \bin" folder. If running this GX interactively, bypassing the menu, first change the folder to point to the "bin" directory, then supply the GX.NET tool in the specified format. See the topic Run GX for more details on running a GX.NET interactively.

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