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<< Click to Display Table of Contents >> Navigation: Velocity > Create depth velocity by well markers and time horizons |
This module constructs a depth-domain interval velocity field by integrating well marker depths with time-domain seismic horizons exported from Petrel. For each stratigraphic horizon present in both the well marker file and the set of Petrel horizon files, the module computes the interval velocity between successive horizons by dividing the depth difference (from the well markers) by the two-way time difference (from the horizon files). The resulting interval velocities are spatially interpolated across the survey area and assembled into a depth-velocity gather at every output bin location.
Use this module when you have well control and interpreted time horizons and need to build a layered interval velocity model in depth for depth conversion, model building, or quality control. The module requires that each Petrel horizon file name encodes the corresponding marker name using a consistent prefix and postfix scheme (for example, To_MarkerName-UNIQ2.phor). Depths below the deepest horizon are filled with the specified bottom velocity. The output is a depth-domain velocity gather that can be viewed as a 2D depth image and used as input to further depth processing workflows.
A bin point vector item that defines the spatial locations (X, Y coordinates) at which the output depth-velocity gather will be computed. This geometry item specifies the trace positions that the output velocity gather will cover. Connect the bin geometry of your target seismic dataset or the output of a binning or grid-calculation module here. The velocity model will be sampled and interpolated at each of these bin locations.
This group contains the core parameters that control the depth range, sampling, and velocity fill of the output model. All parameters in this group work together to define the dimensions and default velocity of the resulting depth-velocity gather.
The maximum depth, in metres, to which the output velocity gather will be built. The gather will contain Max depth / Depth step samples per trace. Set this value to at least the deepest geological target of interest. The default value is 4000 m. Increasing this value extends the model deeper but proportionally increases memory usage and computation time.
The vertical sampling interval of the output depth-velocity gather, in metres. A smaller step produces a finer depth resolution at the cost of a larger output dataset. The default value is 10 m. For most depth conversion workflows a value of 5–20 m is appropriate. Use finer steps only when you need to resolve thin velocity layers accurately.
The velocity value, in m/s, used to fill depth samples that lie below the deepest stratigraphic horizon defined by the well markers and time horizons. This parameter acts as a half-space velocity beneath the lowest constrained layer. Before being applied, this value is multiplied by the Scaler factor. Set it to a geologically reasonable estimate of the velocity below your deepest horizon, for example 3000–5000 m/s for consolidated sedimentary sequences. The minimum allowed value is 0. The default value is 1 m/s (effectively zero fill), so you must set this to a realistic value before running the module.
A dimensionless multiplier applied to all velocity values in the model, including both the interpolated interval velocities and the bottom velocity fill. Use this parameter to apply a global scaling correction — for example, to account for a systematic unit conversion or to adjust velocities from one domain convention to another. A value of 1.0 (the default) leaves velocities unchanged. Values greater than 1 increase all velocities proportionally; values between 0 and 1 reduce them. The minimum allowed value is 0.
A trace vector item that supplies additional geometry metadata required to construct the output gather structure. Connect the trace vector associated with the target seismic survey geometry. This item is used internally to organise the output depth-velocity gather into the correct trace ordering.
The text string that precedes the marker name in each Petrel horizon file name. The module strips this prefix (and the postfix, below) from the horizon file name to extract the marker name, which must exactly match a name in the well markers file. For example, if the horizon file is named To_HorizonA-UNIQ2.phor and the prefix is To_, the extracted marker name will be HorizonA. The default value is To_. Change this to match the naming convention used when exporting horizons from Petrel.
The text string that follows the marker name in each Petrel horizon file name (before the file extension). Together with the prefix, this string defines how the module extracts the marker name from the file name. For example, if the file is named To_HorizonA-UNIQ2.phor and the postfix is -UNIQ2, the extracted marker name is HorizonA. The default value is -UNIQ2. If the module reports that it cannot find a well marker for a given file, verify that the prefix and postfix settings correctly reproduce the marker names as they appear in the well markers file.
The cell size, in metres, of the intermediate spatial grid used to interpolate well marker depths and horizon times across the survey area. The module builds a regular 2D grid at this resolution and fits an approximation-based smooth surface through the scattered input points before sampling the result at each output bin location. The default value is 50 m. Use a smaller value (e.g. 10–25 m) in areas with dense well and horizon coverage to preserve local detail. Use a larger value (e.g. 100–200 m) for sparse datasets or wide-area surveys, where a coarser grid is sufficient and reduces computation time. Setting this value much smaller than the average well spacing will not add meaningful detail and will increase runtime.
The path to an ASCII text file (typically with extension .pmark) containing the well marker data. Each line in the file must contain exactly five whitespace-separated columns in the following order:
WellName MarkerName X Y Depth
where X and Y are the surface coordinates of the well in the survey coordinate system, and Depth is the true vertical depth of the marker in metres (positive downward). Blank lines are skipped. The marker names in this file must match the names extracted from the Petrel horizon file names (after stripping the prefix and postfix). Example line:
Well_12 HorizonA 2260721.11 475926.96 1529.34
A list of Petrel horizon files (typically with extension .phor) exported from Petrel in the standard points-with-attributes format. Each file corresponds to one stratigraphic horizon and must contain a header section ending with the line END HEADER, followed by data rows with three space-separated columns: X, Y, and two-way time in milliseconds. The module reads the two-way time and internally converts it to one-way time in seconds. Add one file per horizon. The file names must follow the naming convention defined by the Prefix and Postfix parameters. Example data rows:
2262722.00 474527.00 -572.03
At least one horizon file is required. The module processes horizons in order of increasing well marker depth, computing interval velocity between each successive pair.
A depth-domain velocity gather containing one trace per output bin location. Each trace holds the interpolated interval velocity as a function of depth, sampled at the specified Depth step from the surface down to Max depth. Within each stratigraphic layer the velocity is constant (equal to the layer interval velocity derived from the well-horizon tie). Below the deepest constrained horizon the trace is filled with Bottom velocity multiplied by Scaler factor. The gather is displayed as a 2D depth image and can be used as input to depth migration, depth conversion, or model quality-control workflows.