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Frac modelling generates a synthetic seismic dataset that simulates the diffraction response of fracture networks or other sub-resolution scattering objects in the subsurface. The module places a set of point diffractors — representing fractures or fracture clusters — at positions derived either from horizon surfaces or from a regular inline/crossline/time grid. For each diffractor, the module computes the travel time from source to scatterer to receiver, scales the amplitude according to geometric spreading and a user-controlled power law, and sums the contribution into the corresponding output trace using a convolution with a user-defined wavelet.
The output is a SEG-Y file containing the modelled seismic data, which can be compared against real pre-stack data to assess whether observed diffraction energy is consistent with a fracture model. An accompanying text file listing the coordinates, two-way times, velocities, and amplitudes of all diffractor positions is written alongside the SEG-Y output to support quality control and visualisation.
Note: This module is deprecated and provided for legacy workflow compatibility. It may be removed or replaced in a future release.
The collection of pre-stack trace headers that defines the survey geometry — source and receiver coordinates, offsets, and datum elevations. The module uses this geometry to calculate the travel-time contribution of each diffractor to each trace. The output synthetic SEG-Y will contain one trace per entry in this collection.
An optional link to an existing SEG-Y dataset. When connected, the module reads the sample count and sample interval from this file, and uses the existing trace data as a starting waveform to which the modelled diffraction energy is added. When not connected, an empty synthetic record is created using the sample geometry derived from the input velocity volume.
A velocity volume (gather) covering the area of interest, typically an interval or RMS velocity field. This input serves two purposes: it defines the spatial grid of bin positions at which diffractors can be placed, and it provides the local velocity value at each diffractor position for use in the travel-time calculation. The sample interval of this volume also sets the output trace sample interval when no SEG-Y handle is connected. This input is mandatory.
An optional migrated seismic volume (gather) used to weight the amplitude of each diffractor. When connected, the module reads the average absolute amplitude in a window around the diffractor's two-way time from this volume and multiplies the base diffractor amplitude by this value. This allows the synthetic fracture response to reflect the local reflectivity or imaging quality of the migrated data. The migration volume must have exactly the same inline/crossline grid and sample interval as the InputVelocity volume.
Controls the shape and bandwidth of the wavelet used to convolve each diffraction travel-time response into the output traces. This parameter group contains three settings:
Wavelet type — selects the wavelet shape. Available options include Ricker1, Ricker2, AKB, Berlage, Gaussian, GaussianDeriv, MinPhase, Klauder, Ormsby, Spike, Zero, and Unit. Ricker1 is the most common choice for synthetic modelling because it produces a compact, zero-phase pulse with clearly defined frequency content.
Frequency — the dominant (peak) frequency of the wavelet, in Hz. Choose a value that matches the dominant frequency of the recorded seismic data so that the synthetic and real events are spectrally comparable.
Wavelet length — the total duration of the wavelet window, in seconds. Set this to at least 3–4 dominant periods to capture the full wavelet without truncation.
Controls the spatial subsampling of bins in the inline direction when placing diffractors on a regular grid (i.e., when no horizon layers are defined). A value of 1 places a diffractor column at every inline; a value of 30 (default) places columns every 30 inlines. Increase this value to reduce computation time and the density of scatterers. This parameter has no effect when horizon layers are used to position the diffractors.
Controls the spatial subsampling of bins in the crossline direction when placing diffractors on a regular grid. A value of 30 (default) places one diffractor column every 30 crosslines. Use together with Inline step to control the total number of scatterers and the resulting computation load. This parameter has no effect when horizon layers are used.
The two-way time interval between consecutive diffractors placed along the time axis at each selected bin, in seconds. The default value is 0.12 s. A smaller interval produces a denser vertical distribution of scatterers and a richer diffraction pattern, but increases computation time. This parameter applies only when no horizon layers are defined.
The earliest two-way time at which diffractors are placed, in seconds. The default is 0 s (the top of the record). Increase this value to exclude shallow, near-surface arrivals from the model and focus the fracture simulation on a particular depth interval of interest.
The latest two-way time at which diffractors are placed, in seconds. The default is 10 s, which is typically much larger than any real record length; in practice this parameter is effectively the end of the trace unless set to a smaller value. Set it to the two-way time of the deepest horizon of interest to avoid placing unnecessary scatterers below the target interval.
The near-surface (replacement) velocity used as the reference medium velocity for the diffraction travel-time calculation, in m/s. The default value is 2000 m/s. This value controls how topographic elevation differences between source, receiver, and diffractor positions are converted into time shifts (datuming corrections), and also enters the Common Reflection Element (CRE) radius calculation that determines the geometric amplitude spreading factor. Set this to the survey replacement velocity or the average near-surface velocity.
The base amplitude assigned to each diffractor before geometric spreading and optional migration-amplitude weighting are applied. The default is 1 (dimensionless). Increase this value to produce a stronger synthetic diffraction signature. When InputMigration is connected, the final diffractor amplitude is the product of AmpValue and the local average absolute amplitude read from the migration volume at the diffractor's time position.
The exponent applied to the geometric amplitude weight when computing the diffraction response for each trace. The default value is 1. The geometric weight is the ratio of the CRE radius to the source-to-scatterer and receiver-to-scatterer distances — values less than 1 indicate the trace is far from the diffractor. Setting AmpPow to 1 applies the weight linearly; values greater than 1 suppress distant, weak contributions more aggressively, concentrating energy on traces that are geometrically close to the scatterer. Set AmpPow to 0 to disable geometric amplitude weighting entirely.
The half-length of the sample window (in samples) used to compute the average absolute amplitude from the InputMigration volume at each diffractor's time position. The default value is 5 samples, meaning amplitudes are averaged over a window of ±5 samples (11 samples total) around the diffractor time. Increase this value if the migration amplitude varies rapidly with time and you want a smoother, more stable amplitude estimate. This parameter has no effect if InputMigration is not connected.
The full file path and base name for the output dataset. The module creates two files using this base name: a SEG-Y file (<name>.sgy) containing the synthetic seismic traces, and a tab-delimited text file (<name>.txt) listing the X, Y, Z coordinates, two-way times, amplitudes, and velocities of all diffractor positions. The text file is useful for visualising and verifying the spatial distribution of the modelled fractures.
A parameter group that allows horizon surfaces to guide the placement of diffractors. When one or more horizons are added to the Layers collection, the module switches from the regular time-grid mode to a horizon-guided mode: diffractors are placed at the interpolated two-way time of each horizon at each selected bin, rather than at fixed time intervals. Use this mode when you want to model fractures constrained to specific geological surfaces (e.g., a fault plane or a reservoir horizon).
A collection of post-stack horizon picks (point vector items). Add one entry for each geological surface along which fractures should be simulated. The two-way time at each bin is determined by spatially interpolating the horizon picks using a fast Kriging algorithm, controlled by MaxDist and MaxPointCount. When this collection is empty, the module falls back to placing diffractors on a regular time grid defined by First time, Last time, and Each time.
The maximum search radius (in metres) used when interpolating horizon picks to estimate the two-way time at each bin. The default is 50 m. Only horizon picks within this distance from the bin centre are used in the Kriging interpolation. If no picks fall within this radius, the diffractor is not placed at that bin. Increase this value for sparsely picked horizons to avoid gaps in the diffractor distribution; decrease it to honour fine-scale structural detail in densely picked areas.
The maximum number of nearby horizon picks used in the Kriging interpolation for each bin. The default is 100. The interpolator selects up to this many nearest picks within the MaxDist radius and computes a weighted estimate of the horizon time. Reducing this number speeds up the interpolation for very dense pick sets but may reduce accuracy. For typical pick densities, the default of 100 is appropriate.