Geometry Steps

 

This section documents the processing steps available in the Geometry category.

 

Processing steps currently available are:

 

 

 

Note Trace Header Geometry Application

 

The first step in the majority of processing sequences is to update the seismic field headers with the acquisition geometry information.  This information is required to perform basic data analysis and to execute almost all multi-channel processing steps.

 

There are three basic structures for the processing flow that is used to update the seismic trace header with the acquisition geometry information.  The structure you use will depend on the nature of the seismic survey.  The three seismic surveys and their associated processing flows can be classified as follows;

 

1.       2D seismic.  In SPW, 2D seismic surveys are those in which the sources and receivers are laid out on the same 2D line and the CMP number can be computed as CMP = (Source Location + Receiver Location) / 2.  This implies that source location 101 and receiver location 101 are co-located (i.e. have the same X,Y coordinates).

 

1.       Crooked line 2D seismic. In SPW, Crooked line 2D seismic surveys are those that will be processed as a single CMP line, though the sources and receivers are not necessarily laid out along the same line.  This implies that source location 101 and receiver location 101 need not be co-located (i.e. are not required to have the same X,Y coordinates).

 

1.       3D seismic.  In SPW, 3D seismic surveys are those in which the sources and receivers are laid out areally and the data will be organized in terms of inlines and crosslines.

 

An example of each of these three types of processing flows can be found in the Templates library under the Geometry category.

 

 

Example Flowchart for a 2D seismic survey:

 

 

 

Example Flowchart for a crooked line 2D seismic survey:

 

 

 

Example Flowchart for a 3D seismic survey:

 

 

Bin Fold Limit

Usage:

The Bin Fold Limit step adds extra flex traces to input binned data from an input Flex Table as output from CMP Binning in flex mode.  Flex traces are selected from the flex table locations as specified by the Bin Fold Limit parameters.

 

An alternative to using CMP Binning in flex mode and Bin Fold Limit to improve coverage is to interpolate the binned data with, for example, 3D Missing Data Interpolation.

 

Input Links:

1)      3D Seismic data sorted by CMP Line and CMP Location, with CMP Location as the record key (mandatory).

2)      Flex Table as output by CMP Binning with flex trace location data.

 

Output Links:

1)      3D Seismic data sorted by CMP Line and CMP Location (mandatory).

 

Reference:

-

 

Example Flowchart:

 

Bin Fold Limit

 

Step Parameter Dialog:

 

Bin Fold Limit params

 

Parameter Description:

 

Trace selection method: Specify the criterion by which traces are selected from both the input data and the flex traces whose locations are specified by the input flex file.

 

Nearest to within bin – If selected, traces will be selected for inclusion in a bin by their distances from the bin boundary.

 

Nearest to bin center – If selected, traces will be selected for inclusion in a bin by their distances from the center of the bin.

 

One trace per offset interval – If selected, this option aims to provide a full range of offsets within each bin by allowing just one trace per offset interval.

 

Override offset interval – If checked, the required offset interval may be overridden in the adjacent box.

 

CMP maximum fold:  This option does not apply when traces are selected for inclusion in a bin by one per offset interval.

 

Maximum traces per bin – Specify the total number of traces that may be included in each bin.

 

Allow removal of non-flex traces – If checked, and there are more (non-flex) traces assigned to a bin than the specified. Maximum traces per bin, then those furthest from the bin center will be removed.  If not checked, then only flex traces which fall within the box will be de-selected.

 

CMP Binning

Usage:

The CMP Binning step assigns CMP line and location numbers according to user specified coordinate parameters. If a 2D survey is specified, you will be prompted to define the line. If a 3D survey is specified, you will be prompted to define the grid.

 

The option of Flex binning allows each bin to contain more traces, by increasing the effective size of each bin and thereby including traces which also fall into neighboring bins. The amount of flex can also be proportional to the trace offset.  The flex traces may be added immediately to the output data flow, or else their locations may be output to a flex file.  This option allows stacking in of the flex traces without extra sorting overhead.

 

Input Links:

1)      Seismic data in any sort order (mandatory).

 

Output Links:

1)      Seismic data in any sort order (mandatory).

2)      Flex table when flex binning (optional).

 

Reference:

-

 

Example Flowchart:

 

CMP Binning

 

Example Flowchart for Flex Binning:

 

CMP Flex Binning

 

 

Step Parameter Dialog for 2D:

 

 

 

Step Parameter Dialog for 3D:

 

 

Step Parameter Dialog for 3D Flex Binning:

 

 

Parameter Description:

 

Line definition (for 2D): Define line parameters. These parameters are exclusive for 2D surveys.

 

Start of line easting (for 2D) — Enter the start of line easting.

 

Start of line northing (for 2D) — Enter the start of line northing.

 

End of line easting (for 2D) — Enter the end of the line easting.

 

End of line northing (for 2D) — Enter the end of the line northing.

 

Line number (for 2D) — Enter the line number.

 

Line azimuth (for 2D) — Enter the line azimuth.

 

First midpoint number (for 2D) — Enter the first midpoint number.

 

Common midpoint increment (for 2D) — Enter the common midpoint increment.

 

Common midpoint size (for 2D) — Enter the common midpoint size.

 

Grid definition (for 3D) — Define the 3D grid. These parameters are exclusive for 3D surveys.

 

Corner 1 – Easting (for 3D) — Enter the easting (x) coordinate of the first corner of your survey.

 

Corner 1 – Northing (for 3D) — Enter the northing (y) coordinate of the first corner of your survey.

 

Corner 2 – Easting (for 3D) — Enter the easting (x) coordinate of the second corner of your survey.

 

Corner 2 – Northing (for 3D) — Enter the northing (y) coordinate of the second corner of your survey.

 

Corner 3 – Easting (for 3D) — Enter the easting (x) coordinate of the third corner of your survey.

 

Corner 3 – Northing (for 3D) — Enter the northing (y) coordinate of the third corner of your survey.

 

Inline bin size (for 3D) — Enter the size in distance units of the in-line side (1 to 2) of each bin.

 

Crossline bin size (for 3D) — Enter the size in distance units of the cross-line side (1 to 3) of each bin.

 

First inline number (for 3D) — Enter the first inline number. This line number is assigned to all the bins along the side of the survey from corner 1 to corner 2.

 

Inline increment (for 3D) — Enter the increment in line numbers between adjacent CMP lines.

 

First crossline number (for 3D) — Enter the first crossline number. This location number is assigned to all the bins along the side of the survey from corner 1 to corner 3.

 

Crossline increment (for 3D) — Enter the increment in locations between adjacent CMP locations.

 

Coordinate definition: Specify whether the corner points define the bin centers or corners following the figure below.

 

 

Corner points define bin centers — If selected, specify that corner points define bin centers.

 

Corner points define bin corners — If selected, specify that corner points define bin corners.

 

 

Survey dimensions: Specify whether the dimensions of the survey are 2D or 3D.

 

2D — If selected, specify 2D line survey.

 

3D — If selected, specify a 3D grid survey.

 

Project updates: Specify project updates.

 

Update from project — Select to update from the project.

 

Update project — Select to update the project.

 

Binning type specification: Specify standard binning or the type of flex binning.

 

No flex binning — If selected, a standard binning, with no extra traces added, is going to be performed.

 

Output flex traces directly — If selected, add flex traces to the output binned traces.

 

Output flex locations to a flex file — If selected, add the locations of flex traces to an additional output flex file. The flex traces may then be added using Bin Fold Limit at a later stage.

 

Flex binning specification: Specify standard binning or the type of flex binning.

 

Inline % bin flex — Enter the percentage increase of each bin size in the inline direction to include extra ‘flex’ traces.

 

Crossline % bin flex — Enter the percentage increase of each bin size in the crossline direction to include extra ‘flex’ traces.

 

Inline % Offset flex — Enter the increase of each bin size as the percentage increase of the trace inline offsets.

 

Crossline % Offset flex — Enter the increase of each bin size as the percentage increase of the trace crossline offsets.

 

Note: The bin flex and Offset flex options are additive – the bin size used will be the maximum size of the bin flex and Offset flex options.

 

CMP Fold - Data

Usage:

The CMP Fold – Data step extracts information related with the CMP fold from the seismic data trace headers.

 

Input Links:

1) Seismic data in any sort order (mandatory).

 

Output Links:

None

 

Reference:

-

 

Example Flowchart:

 

.4

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Bin fold file name — Select file to save the bin fold map in bsf form.

 

Specify an offset range — If checked, CMP fold map is limited by minimum and maximum offset distance as it is written in the trace headers.

 

                Minimum offset — Enter the minimum offset considered to build the CMP fold map.

 

                Maximum offset — Enter the maximum offset considered to build the CMP fold map.

 

Specify an azimuth range — If checked, CMP fold map is limited by minimum and maximum azimuth defined in degrees from the North.

 

                Minimum azimuth (deg.) — Enter the minimum azimuth considered to build the CMP fold map.

 

                Maximum azimuth (deg.) — Enter the maximum azimuth considered to build the CMP fold map.

 

Map area: Define map area either by survey of data.

 

                Survey — If selected, the CMP fold map is built from survey geometry.

 

                Data — If selected, the CMP fold map is built from data geometry.

 

 

Coordinate Conversion

Usage:

The Coordinate Conversion step allows converting the coordinates stored in the seismic traces headers between geographic (latitude/longitude), Transverse Mercator, UTM or UPS. This step allows converting the source, receiver and CMP coordinates simulatenously or individually.

 

Input Links:

1)      Seismic data in any sort order (mandatory).

 

Output Links:

1)      Seismic data in any sort order (mandatory).

 

Reference:

-

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Input file coordinate system: Specify the coordinate system of the input seismic file.

 

Geographic (Lat-Long) — Select the coordinate system. The user may choose between Geographic (latitude/longitude), Transverse Mercator, UTM – Universal Transverse Mercator or UPS – Universal Polar Stereographic.

 

Geographic units (only for Geographic (Lat-Long)) — Select if the geographic coordinates are in Decimal or DD MM SS.

 

Geographic datum — Select the datum of the selected coordinate system. Only available for Transverse Mercator, UTM and UPS.

 

Orientation – longitude — Select between East or West.

 

Hemisphere – latitude — Select the hemisphere of the coordinate system.

 

Override input geographic datum values — If checked, overrides the standard parameters of the selected coordinate reference system.

 

                Equatorial radius (m) — Enter the value in meters for the user-defined equatorial radius.

 

                Polar radius (m) — Enter the value in meters for the user-defined polar radiues.

 

                Mean radius (m) — Enter the value in meters for the user-defined mean radius.

 

                Flattening — Enter the value for flattening.

 

                Flattening reciprocal — Enter the flattening reciprocal values.

 

                Scale — Enter the scale factor.

 

                Eccentricity — Enter the eccentricity value.

 

Override input central meridian — If checked, overrides the central meridian for the input coordinate reference system.

 

                Input central meridian — Enter the value for the user-defined central meridian.

 

Output file coordinate system: Specify the coordinate system of the input seismic file.

 

Geographic (Lat-Long) — Select the coordinate system. The user may choose between Geographic (latitude/longitude), Transverse Mercator, UTM – Universal Transverse Mercator or UPS – Universal Polar Stereographic.

 

Geographic units (only for Geographic (Lat-Long)) — Select if the geographic coordinates are in Decimal or DD MM SS.

 

Geographic datum — Select the datum of the selected coordinate system. Only available for Transverse Mercator, UTM and UPS.

 

Orientation – longitude — Select between East or West.

 

Hemisphere – latitude — Select the hemisphere of the coordinate system.

 

Override output geographic datum values — If checked, overrides the standard parameters of the selected coordinate reference system.

 

                Equatorial radius (m) — Enter the value in meters for the user-defined equatorial radius.

 

                Polar radius (m) — Enter the value in meters for the user-defined polar radiues.

 

                Mean radius (m) — Enter the value in meters for the user-defined mean radius.

 

                Flattening — Enter the value for flattening.

 

                Flattening reciprocal — Enter the flattening reciprocal values.

 

                Scale — Enter the scale factor.

 

                Eccentricity — Enter the eccentricity value.

 

Override output central meridian — If checked, overrides the central meridian for the output coordinate reference system.

 

                Output central meridian — Enter the value for the user-defined central meridian.

 

Convert source coordinates — If checked, apply coordinate conversion to source coordinates.

 

Convert receiver coordinates — If checked, apply coordinate conversion to receiver coordinates.

 

Convert CMP coordinates — If checked, apply coordinate conversion to CMP coordinates.

 

Crooked Line Binning

Usage:

The Crooked Line Binning step selects those traces from an input 3D pre-stack seismic data file whose source-receiver mid-points fall sufficiently close to the centers of bins following a crooked line defined by 3D locations in a Line Definition card data file.  The input data mid-points are calculated from the source and receiver eastings and northings placed in the trace headers though the use of SPS files by Geometry Definition. The Line Definition card data file contains the eastings and northings of crooked line CMP positions of a best-fit line determined by Crooked Line Fit.

 

Input Links:

1)      3D Seismic data in any sort order (mandatory).

2)      Line Definition card data file (mandatory).

 

Output Links:

1)      Crooked line 2D CMP binned seismic data in any sort order (mandatory).

 

Reference:

-

 

Example Flowchart:

Crooked Line Binning

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Number of first midpoint — Enter the number of the first midpoint.

 

In line bin dimension (ft or m) — Enter the inline bin dimension.

 

Line width (ft or m) — Enter the crossline bin dimension.

 

Project updates: These keys allow values to be read from the project, or alternatively to update the project.

 

Update from project — Select to update from the project.

 

Update project — Select to update the project.

 

Output data CMP coordinates: Specify if output coordinates are bin coordinates or source-receiver midpoints.

 

Bin coordinates — If selected, those traces which fall into crooked line bins and output will be given CMP coordinates which reflect the center points of the bins.

 

Source-receiver coordinates — If selected, those traces which fall into crooked line bins and output will be given CMP coordinates equal to their source-receiver nid-points.

 

Source and Receiver Binning: Specify if the binning is performed at source or receiver locations.

 

Bin source locations — If checekd, those traces whose source locations fall into crooked line bins will be output.

 

Bin receiver locations — If checked, those traces whose receiver locations fall into crooked line bins will be output.

 

Flex Binning: Specify the flex binning parameters.

 

Use flex binning — If checekd, those traces whose source locations fall into or sufficiently close to crooked line bins will be output.

 

In-line % flex — Enter the percentage distance from a trace mid-point to the boundary of a bin as compared to the bin width for that trace to be considered valid and output as a flex trace.

 

Extract Geometry

Usage:

The Extract Geometry step extracts geometry information from the seismic trace header and create source, receiver SPS card data files or UKOOA P190 Locations card data file.

 

Input Links:

1) Seismic data in any sort order (mandatory).

 

Output Links:

1)      Source SPS card data file (mandatory).

2)      Receiver SPS card data file (mandatory).

 

Or

 

3)      Observer SPS card data file (UKOOA P190 Locations).

 

Reference:

-

 

Example Flowchart:

 

 

Or

 

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Output source SPS file — If checked, output source coordinates of the input seismic file in a source SPS card data file.

 

Output receiver SPS file — If checked, output receiver coordinates of the input seismic file in a receiver SPS card data file.

 

Output marine P1/90 file — If checked, output coordinates of the input seismic file in a marine UKOOA P190 card data file.

 

Warning for non-UTM range of coordinates — If checked, warns if the UTM range of coordinates is null.

 

Geometry Definition

Usage:

The Geometry Definition step assigns survey information to the trace headers based on the source, receiver, and observer notes SPS files.  The Geometry Definition step assigns CMP number based on the source and receiver numbers using the following formula:  CMP Location = (Source Location + Receiver Location).  Therefore, for 2D lines it is imperative that source and receiver locations as defined in the SPS files share the same coordinate system.  This implies that Source location 1 has the same X,Y position as Receiver location 1, and that Source location 2 has the same X,Y position as Receiver location 2, etc…  In the case of 3D data, this is not an issue, as CMP Line and Location will be labeled by the CMP Binning step.  

 

Input Links:

1) Seismic data in any sort order (mandatory).

2) Observers Notes – SPS Format cards (mandatory).

3) Receiver Locations – SPS Format cards (mandatory).

4) Source Locations – SPS Format cards (mandatory).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

References:

-

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Kill undefined traces and records — If checked, any traces or records that are not represented in the SPS files will be marked as dead.

 

Use unsigned offsets — If checked, the offset values written to the seismic header will be unsigned.

 

Define survey orientation for signed offsets — If checked, the sign on offset values will be adjusted for the orientation of the dominant receiver line azimuth, such that offset up-the-spread will be positive, and offsets down-the-spread will be negative.

 

Enter survey orientation (degrees) — Enter the value of the survey orientation in degrees.

 

Assign trace header statics from SPS files — If checked, trace header statics are assigned from auxiliary SPS files.

 

Use unsigned azimuths — If checked, the azimuth values written to the seismic header will range from 0 to 360 degrees, with zero degrees of azimuth equal to the user-specified direction.  By default, azimuth values are signed and range from 0 to +/-180 degrees, with zero degrees of azimuth equal to the user-specified direction.

 

Use source and receiver index number — Define source and receiver by its index number.

 

Azimuth definition: Specify the origin of azimuth.

 

Zero degrees azimuth = East — If selected, then zero degrees of source-receiver azimuth will be set equal to due East.

 

Zero degrees azimuth = North — If selected, then zero degrees of source-receiver azimuth will be set equal to due North.

 

 

Definition of azimuths using the Geometry Definition parameters.

 

Nominal receiver interval — Enter the nominal interval between receiver stations in distance units.

 

 

Geometry Definition Example:

 

 

Figure 1. 2D seismic survey consisting of a 6-channel spread and a 25-m station interval.  The spread “rolls-off” at the end of the line.

 

Source SPS file corresponding to the survey illustrated in figure 1.

 

Figure 3.  Receiver SPS file corresponding to the survey illustrated in figure 1.

 

 

 

 

 

 

 

Figure 4.  Observer SPS file corresponding to the survey illustrated in figure 1.

 

OBS Positioning

Usage:

The OBS Positioning step accurately estimate the Ocean Bottom Seismometer (OBS) position (x,y,z) from knowledge of the sources locations and the picked first arrivals.

 

Input Links:

1)      Seismic file from receiver gathers recorded with the OBS instrument, with source Easting/Northing/Elevation header information (mandatory).

2)      First Break times - Pick First arrival picks (optional).

 

Output Links:

1)      Seismic file from receiver gathers with the computed receiver Easting/Northing/Elevation (mandatory).

 

References:

-

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

First arrival picks: Specify first arrival times picks parameters.

 

Use first arrivals from header word — if checked select the header word containing the first arrivals information.

 

Use first arrivals from card date — if checked a first arrivals card data will connect to the step.

 

Receiver/Source paramters: Specify source elvation parametes.

 

Sources are mainly at the same depth — if checked all sources are at the same depth range.

 

Velocity check: Specify range of water velocity.

 

Check range of the computed water velocity — return a warning message if the inverted velocity exceeds a range specified by the Minimum/Maximum velocities.

 

Minimum velocity — Enter minimum velocity for water column.

Maximum velocity — Enter maximum velocity for water column.

 

Offset Binning

Usage:

The Offset binnig step bins the input seismic file by the offset defined in the header of the seismic traces.

 

Input Links:

1)      Seismic data in any sort order (mandatory).

 

Output Links:

1)      Seismic data in any sort order (mandatory).

 

References:

-

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Offsets type:

Absolute values —

Signed offsets —

 

Offsets bin specification:

Bin size —

Bin boundaries zero-offset based —

Bon mid-point zero-offset based —

 

Set offsets to bin center offset —

 

Project updates: Specify project updates.

 

Update from project — Select to update from the project.

 

Update project — Select to update the project.

 

Simple Marine Geometry

Usage:

The Simple Marine Geometry step assigns geometry information to the seismic trace headers based for simple 2D marine seismic acquisition.

 

Input Links:

1.       Seismic data in any sort order (mandatory).

2.       Streamer Definition card data (mandatory).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

 

References:

-

 

Example Flowchart:

 

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Source locations: Specify location of sources.

 

Source location equals field file number — If selected, source locations are set equal to field file number from seismic trace headers.

 

Use trace header source location number, northing, easting — If selected, source locations are set equal to source location (number, northing and easting) grom the trace headers.

 

Manually define source location numbers — If selected, source locations are defined manually from the parameters below.

 

Use SPS formatted observers (XPS) file — If selected, source locations are set as defined in the auxiliare observers (XPS) card data file.

 

Source line number — Enter the source location line number.

 

Source location number of first field file — Enter the location of the source for first field file number.

 

Source location increment — Enter the source location increment. This value must be an integer value.

 

Distance between shot (ft or m) — Enter the distance between shots in ft or m, depending on the units defined for the project.

 

Source-to-near-channel offset (ft or m) — Enter the near offset, distance between source and the near channel. Distance defined in ft or m, depending on the units defined for the project.

 

Lateral source offset (perpendicular) — Enter the offset distance in the direction perpendicular to the streamer.

 

Group interval (ft or m) — Enter the distance between each group. Distance defined in ft or m, depending on the units defined for the project.

 

Channel number of near offset group — Enter the number of the enear offset group.

 

Channel number increment — Enter the increment between channels.

 

Number of channles — Enter total number of channels in the streamer.

 

Receiver location increment — Enter the increment between receiver locations.

 

Use SPS formatted source locations file — If checked, source locations are extracted from an auxiliary source SPS card data file.

 

UKOOA P1/90 Geometry

Usage:

The UKOOA P1/90 Geometry step assigns survey information to the trace headers based on a geometry file as defined in an auxiliary UKOOA P1/90 card data file.

 

Input Links:

1) Seismic data in any sort order (mandatory).

2) UKOOA P1 90 card data file (mandatory).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

References:

-

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

 

 

Parameter Description:

 

Source line number — Enter the source/sail line number corresponding to the selected P1/90 coordinate file.

 

Nominal channel interval — Enter the spacing between channels on the cable.

 

Nominal source interval — Enter the spacing between sources.

 

Starting CMP location — Enter the intial CMP location.

 

Data dimension: Specify data dimensions.

 

2D survey — If selected, input seismic file is a 2D survey.

 

3D survey — If selected, input seismic file is a 3D survey.

 

Update Marine Streamer

Usage:

The Update Marine Streamer step allows the update of the streamer configuration of an existing geometry already defined on the input seismic data.

 

Input Links:

1) Seismic data in any sort order (mandatory).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

References:

-

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Distance between shots (ft or m) — Enter the distance between shots. Distance defined in ft or m, depending on the units defined for the project.

 

Source-to-near channel offset (ft or m) — Enter the distance between source and the near channel. Distance defined in ft or m, depending on the units defined for the project.

 

Group interval (ft or m) — Enter the distance between groups. Distance defined in ft or m, depending on the units defined for the project.

 

Channel number of near offset group — Enter the number of the channel for the near offset group.

 

Channel number increment — Enter the increment between the channel number.

 

Number of channels — Enter the total number of channels.

 

Update Receiver Positions

Usage:

The Update Receiver Positions step allows updating the position of the receivers, as defined in the auxiliary SPS Receiver Locations card data file, of the input seismic data file.

 

Input Links:

1) Seismic data in any sort order (mandatory).

2) Auxiliary SPS Receiver Locations card data file (mandatory).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

References:

-

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Use unsigned offsets — If checked, the offset values written to the seismic header will be unsigned.

 

Define survey orientation for signed offsets — If checked, the sign on offset values will be adjusted for the orientation of the dominant receiver line azimuth, such that offset up-the-spread will be positive, and offsets down-the-spread will be negative.

 

Enter survey orientation (degrees) — Enter the value of the survey orientation in degrees.

 

Use unsigned azimuths — If checked, the azimuth values written to the seismic header will range from 0 to 360 degrees, with zero degrees of azimuth equal to the user-specified direction.  By default, azimuth values are signed and range from 0 to +/-180 degrees, with zero degrees of azimuth equal to the user-specified direction.

 

Azimuth definition: Specify the origin of azimuth.

 

Zero degrees azimuth = East — If selected, then zero degrees of source-receiver azimuth will be set equal to due East.

 

Zero degrees azimuth = North — If selected, then zero degrees of source-receiver azimuth will be set equal to due North.

 

Nominal receiver interval — Enter the nominal interval between receiver stations in distance units.

 

Update Source Positions

 

Usage:

The Update Source Positions step allows updating the position of the sources, as defined in the auxiliary SPS Source Locations card data file, of the input seismic data file.

 

Input Links:

1) Seismic data in any sort order (mandatory).

2) Auxiliary SPS Source Locations card data file (mandatory).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

References:

-

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Use unsigned offsets — If checked, the offset values written to the seismic header will be unsigned.

 

Define survey orientation for signed offsets — If checked, the sign on offset values will be adjusted for the orientation of the dominant receiver line azimuth, such that offset up-the-spread will be positive, and offsets down-the-spread will be negative.

 

Enter survey orientation (degrees) — Enter the value of the survey orientation in degrees.

 

Use unsigned azimuths — If checked, the azimuth values written to the seismic header will range from 0 to 360 degrees, with zero degrees of azimuth equal to the user-specified direction.  By default, azimuth values are signed and range from 0 to +/-180 degrees, with zero degrees of azimuth equal to the user-specified direction.

 

Azimuth definition: Specify the origin of azimuth.

 

Zero degrees azimuth = East — If selected, then zero degrees of source-receiver azimuth will be set equal to due East.

 

Zero degrees azimuth = North — If selected, then zero degrees of source-receiver azimuth will be set equal to due North.

 

Migration Steps

 

This section documents the processing steps available in the Migration category.

 

The types of migration currently available are:

 

 

 

2D Paraxial Ray Tracing

Usage:

The 2D Paraxial Ray Tracing step is an asymptotic wave method, which uses quantities (local wavefront curvature and spreading information) determined along a central ray via dynamic ray tracing, to evaluate approximately the seismic wave field in its vicinity rather then just on the ray itself (Cerveny et al. 1984). This implementation is designed to run in single thread or in parallel, giving it the possibility to take full advantage of multiple processors at the same time.

Input Links:

-

 

Auxiliary dataset:

1)      Interval Velocity-Field file, created using the step Create Velocity Field under the velocity category (mandatory).

2)      Pre-stack dataset, used to get source and receivers geometry (mandatory).

 

Output Links:

1) Seismic file where the computed source or receiver travel-time tables will be saved (mandatory).

 

References:

Cerveny V, Klimes L, Psencik I (1984) Paraxial ray approximations in the computation of seismic wavefields in inhomogeneous media. Geophys J R Astron Soc 89–104.

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Source/Receiver parameters: Specify source or receiver parameters.

 

Run a source ray tracing — If selected, shoot rays at source locations.

 

Run a receiver ray tracing — If selected shoot rays at receiver locations.

 

Use Recording surface other than zero — If checked, specify the header word containing the source elevation information.

 

Source elevation — Select the trace header word containg the elevation information.

 

Travel-time tables: Specify the geometry related with the travel time table used for the 2D paraxial ray tracing.

 

Set up travel-time tables geometry — If checked, defines the travel-time tables geometry. If not checked, the geometry of the input velocity file information is used as reference.

 

First depth sample — Enter the first depth sample in the travel-time table.

 

Depth interval — Enter the depth interval in the travel-time table.

 

First lateral sample — Enter the first lateral sample in the travel-time table.

 

Lateral interval — Enter the lateral interval in the travel-time table.

 

Ray tracing parameters: Specify the ray tracing parameters.

 

Time sample interval — Enter the time sample interval in ray tracing.

 

Number of time samples — Enter the number of time samples in ray tracing.

 

Number of rays — Enter the number of rays.

 

Set in-line aperture — Define the setting for the in-line aperture. If not checked, the maximum aperture is used, which require more compute time.

 

In-line aperture — Enter the ray tracing aperture for the in-line direction.

 

First take-off angle of rays (deg.) — Enter the first take-off angle of the rays in degrees.

 

Increment of take-off angle — Enter the increment of the take-off angle.

 

Minimum emergence angle — Enter the minimum emergence angle.

 

Maximum emergence angle — Enter the maximum emergence angle.

 

Extrapolation radius factor — Enter the factor to determine the radius for extrapolation.

 

Solve eikonal equation in shadow zones — If checked implements the eikonal equation in the shadow zones.

 

2D Pre-Stack PSPI Migration

Usage:

The 2D Pre-Stack PSPI Migration step is only available for 2D seismic data and is a 2D ‘Phase Shift Plus Interpolation’ seismic data migration. The input data must be in the form of frequency slices of CMP v Offset. Convert the CMP and offset-sorted data to frequency slices by the use of Frequency Slices step in a prior job flow.

 

The output data will be in standard trace order and not requiring further transformation.

 

Input Links:

1) Frequency slices ordered by Slice Number and CMP (mandatory).

 

Output Links:

1) Time traces sorted by CMP and Offset (mandatory).

 

Reference:

Gasdag, J, and Sguazzero P., 1984, Migration of seismic data by phase shift plus interpolation, Geophysics, vol. 49, no. 2, p. 124-131.

 

Popovici, A.M., 1996, Pre-stack migrationby split-step DSR, Geophysics, vol. 61, no. 5, p. 1412-1416..

 

 

Example Flowchart:

 

2D Pre-Stack PSPI Migration

 

Step Parameter Dialog:

 

2D Pre-Stack PSPI Migration params

 

 

Parameter Description:

 

Migration mode: Specify migration domain and output format.

 

Time Migration — If checked, time migration will be performed.

 

Output maximum time(ms) — Enter the maximum time of the output migrated data in milliseconds. The time sampling will be the same as that of the input data.

 

Depth Migration — If checked, depth migration will be performed.

 

Output maximum depth(ft/m) — Enter the maximum depth of the output migrated data.

 

Output depth sampling (ft/m) — Enter the depth sampling interval of the output migrated data.

               

Migration velocity field: Specify parameters related with the velocity field used for migration.

 

Use velocity field from data file — If checked, then the file name of an auxiliary input file must be specified which contains the velocity field picks.

 

Use constant migration velocity — If checked, then the migration velocity to be used should be specified in the adjacent box.

 

Scale input velocities by — The migration velocities may be scaled by a constant factor if required.

 

Velocity sampling: Specify velocity sampling parameters.

 

Use CMP velocity — If selected, then velocity will be CMP dependent only. This is the normal assumption when performing time migration.

 

[Use velocity from CMP and offset — If selected, then velocity field will be expected to be dependent both on CMP and on offset. This is likely to be the case when performing depth migration. This option is not currently available.]

 

Migration step size: Specify migration step size.

 

Number of output samples — Enter the number of output migration slices to be output with each iteration of the migration.  Every migration iteration takes a roughly constant execution time, so the total execution time can be significantly reduced if several output slices are calculated at once. There may be a degradation in the migration of dipping data if this parameter is set too high. Consequently, this parameter is data-dependent and may require testing.

 

Frequency filtering: Specify filtering parameters. The output migrated data will be Hanning (cosine) tapered.

 

Low cut Frequency (Hz.) — Enter the low cut frequency of the output migrated data.

 

Low pass Frequency (Hz.) — Enter the low pass frequency of the output migrated data.

 

High pass Frequency (Hz.) — Enter the high pass frequency of the output migrated data.

 

High cut Frequency (Hz.) — Enter the high cut frequency of the output migrated data.

 

Alias energy removal: Specify alias energy removal.

 

Evanescent damping factor — Enter the amount of suppression of energy which is not a real solution of the acoustic wave equation, as a value between zero and one. A value of 0.5 is recommended.

 

Spatial padding width (traces) — Enter how many additional traces are to be added (in both CMP line and location directions in the case of 3D migration).  These extra traces plus spatial tapering help to minimize interference of migrated energy from one end of the data into migrated data on the other side.

 

Override trace spacing: Specify if the original trace spacing is override by a user defined distance. If the trace spacing cannot be read from or is incorrect in the trace headers, then it may be specified in the following parameter fields:

 

Specify the CMP spacing— If checked, then the user must enter the distance between CMP locations in the adjacent field.

 

3D Finite Differences Ray Tracing

Usage:

The 3D Finite Differences Ray Tracing step is a wavefront tracing technique, and a robust alternative to conventional ray tracing. This method relies on the application of Huygens’ Principle in the finite difference approximation. That is, every point reached by a wave becomes a secondary source; the sum of these secondary waves determines the form of the wave at any subsequent time. This method accurately computes travel-time information even with step velocity contrast as high as 1:10 regardless of the sharpness of the velocity anomaly. This implementation is designed to run in single thread or in parallel, giving it the possibility to take full advantage of multiple processors at the same time.

Input Links:

-

 

Auxiliary dataset:

1)      3D Interval Velocity-Field file, created using the step Create Velocity Field under the velocity category (mandatory).

 

2)      Pre-stack dataset, used to get source and receivers geometry (mandatory).

 

Output Links:

1)      Seismic file where the computed source or receiver travel-time cubes will be saved (mandatory).

 

References:

Podvin P, L. I (1991) Finite difference computation of traveltimes in very contrasted velocity models: a massively parallel approach and its associated. Geophys J Int 105:271–284.

Huygens wavefront tracing: A robust alternative to conventional ray tracing. SEP Report, 95, 101-113 (1997)

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

Source/Receiver parameters: Specify source or receiver parameters.

 

Run a source ray tracing — If selected, shoot rays at source locations.

 

Run a receiver ray tracing — If selected, shoot rays at receiver locations.

 

Define the travel time computation grid (m) — If checked, specify the grid spacing on which the computation is carried; the output grid is exactly the same as the velocity grid.

               

                Travel time grid spacing (m) — Enter the travel time grid spacing.

 

Use Recording surface other than zero — If checked, specify the header word containing the source elevation information.

 

                Source/Receiver elevation — Select header word with source elevation information.      

 

Mute above the source/receiver depth — This option is only enabled if the recording surface is other then zero.

 

Constant Velocity PSKTM

Usage:

The Constant Velocity PSKTM step is a migration velocity analysis tool; it runs multiple Pre-Stack Kirchhoff Migrations around the velocity model given as input to pick the velocity that migrate best the data. This implementation is designed to run in single thread or in parallel, giving it the possibility to take full advantage of multiple processors at the same time.

 

Input Links:

1)      Pre-Stack seismic dataset with geometry applied to it and preferably some pre-processing as well (mandatory).

 

Auxiliary dataset:

1)      Velocity model/function (mandatory).

 

Output Links:

1)      Seismic file where the Constant Velocity PSKTM will be saved (mandatory).

 

References:

-

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Migration limits: Specify the migration limits for the constant velocity migrations.

 

Migrate zero samples — If checked, samples with amplitudes value zero will be migrated as well.

 

Constant Start time (ms) — If checked, defines a constant migration start time.

 

Constant end time (ms) — If checked, defines a constant migration end time.

 

Limit operator dip — If checked, limits the dip angle of the migration operator.

 

Minimum offset (m) — If checked, defines a minimum offset for the migration operator.

 

Maximum offset (m) — If checked defines a maximum offset for the migration operator.

 

Migration velocities: Specify the parameters related with the velocities.

 

First Velocity (m/s) — Enter the first velocity to be considered for migration.

 

Velocity Increment (m/s) — Enter the velocity increment.

 

Number of Velocities — Enter the number of velocities to be tested.

 

Number of Velocities — Enter the number of velocities to be tested.

 

Velocity window (m/s) — Enter a window around the input velocity model.

 

Traveltime calculations: Specify parameters for traveltime calculations.

 

Assuming a flat topography scenario — If selected, assume a flat recording surface when computing travel-time information.

 

Accounting for rugged topography — If selected, assume a rugged recording surface when computing travel-time information.

 

Convert Time to Depth

Usage:

The Convert Time to Depth step does a vertical time to depth conversion of a seismic file using an input set of interval velocities.  The input velocities are assumed to be in units of feet or meters per second.  If the input file to be depth converted is a GPR image, and the input velocity file is in units of feet or meters per nanosecond, you must first multiply the velocity values by 1x10-9

 

Input Links:

1) Seismic data in any sort order (mandatory).

2) Velocity Function cards (optional).

 

Output Links:

1) Seismic data in any sort order (mandatory).

 

References:

See Technical Note TN-DpthConv.doc

 

Example Flowchart:

 

 

 

 

Step Parameter Dialog:

 



Parameter Description:

 

Velocity field estimation: Specify velocity field.

 

Use velocity field from data file — If selected, the velocity field used for the time to depth conversion is from an auxiliary velocity field card data.

 

Use smooth velocities — If selected, input velocities are smoothed horizontally and vertically.

 

Use blocky velocities — If selected, input velocities are converted into interval velocities.

 

Correction velocity — Enter the correction velocity (ft/sec or m/sec) to be used in the conversion. This constant velocity will be used unless a velocity function is connected to the step.  In the case of GPR data, convert this value to the appropriate units.

 

Output depth interval — Enter the depth interval in your spatial units.  To obtain an estimate of the output depth interval, first employ the formula X = VT, where X = estimated depth of section, V = average velocity of section, and T = one-way time of the section (i.e. record length divided by two).  Second, employ the formula output depth interval = DX = X/(number of samples   1).

 

Number of output samples — Enter the number of samples to output.

 

Interpolation Type Selection — Select the type of interpolator to use. This interpolator is used to resample the data to the specified depth interval.

 

Do inverse correction — If checked, a depth to time conversion will be performed.

 

 

FK Dip Moveout

Usage:

Input Links:

Output Links:

Reference:

-

Example Flowchart:

Step Parameter Dialog:

Parameter Description:

 

PSPI Migration

Usage:

The PSPI Migration step is a post-stack ‘Phase Shift Plus Interpolation’ seismic data migration.

Input data may be 2D or 3D, and both time migration and depth migration are options.

 

The input data must be in the form of frequency slices – data can be converted to frequency slices by the use of Frequency Slices in a prior job flow.

 

The output data will be in the form of time slices – convert the time slices back to standard trace order in a subsequent job flow after the migration with the use of Time Slices to Traces.

 

Input Links:

1) Frequency slices ordered by Slice Number and CMP Line (3D) or by Slice Number (2D) (mandatory).

 

Output Links:

1) Time slices (or depth slices) ordered by Slice Number and CMP Line (3D) or by Slice Number (2D) (mandatory).

 

Reference:

Gasdag, J, and Sguazzero P., 1984, Migration of seismic data by phase shift plus interpolation, Geophysics, vol. 49, no. 2, p. 124-131.

 

 

Example Flowchart:

 

PSPI Migration

 

Step Parameter Dialog:

 

 

 

Parameter Description:

 

Migration mode: Define type o migration (time or depth migration) to be applied to data.

 

Time Migration — If checked, time migration will be performed.

 

Output maximum time(ms) — Enter the maximum time of the output migrated data in milliseconds. The time sampling will be the same as that of the input data.

 

Depth Migration — If checked, depth migration will be performed.

 

Output maximum depth(ft/m) — Enter the maximum depth of the output migrated data.

 

Output depth sampling (ft/m) — Enter the depth sampling interval of the output migrated data.

 

Migration velocity field: Specify the type of velocity field to be applied during the migration.

 

Use velocity field from data file — If checked, then the file name of an auxiliary input file must be specified which contains the velocity field picks.

 

Use constant migration velocity — If checked, then the migration velocity to be used should be specified in the adjacent box.

 

Scale input velocities by — The migration velocities may be scaled by a constant factor if required.

 

Output velocity field only— If checked, then only the interpolated and fully sampled migration velocity will be output. This flag is for test purposes only.

 

Migration step size: Specify the step size for the migration.

 

Number of output samples — Enter the number of output migration slices to be output with each iteration of the migration.  Every migration iteration takes a roughly constant execution time, so the total execution time can be significantly reduced if several output slices are calculated at once. There may be a degradation in the migration of dipping data if this parameter is set too high. Consequently, this parameter is data-dependent and may require testing.

 

Frequency filtering: Specify and parameterizer the frequency filter to be applied to the migrated data. The output migrated data will be Hanning (cosine) tapered.

 

Low cut Frequency (Hz.) — Enter the low cut frequency of the output migrated data.

 

Low pass Frequency (Hz.) — Enter the low pass frequency of the output migrated data.

 

High pass Frequency (Hz.) — Enter the high pass frequency of the output migrated data.

 

High cut Frequency (Hz.) — Enter the high cut frequency of the output migrated data.

 

Alias energy removal: Specify parameters related with alias energy removal.

Evanescent damping factor — Enter the amount of suppression of energy which is not a real solution of the acoustic wave equation, as a value between zero and one. A value of 0.5 is recommended.

 

Spatial padding width (traces) — Enter how many additional traces are to be added (in both CMP line and location directions in the case of 3D migration).  These extra traces plus spatial tapering help to minimize interference of migrated energy from one end of the data into migrated data on the other side.

 

Override trace spacing: If the trace spacing cannot be read from or is incorrect in the trace headers, then it may be specified in the following parameter fields.

 

Specify the trace spacing — If checked, enter the distance between trace locations.

 

Specify the line spacing — If checked, enter the the distance between lines (for 3D data only).

 

Phase Shift Migration

Usage:

The Phase Shift Migration step implements a constant velocity or a depth-variable velocity post stack phase shift time migration in the frequency domain. The input velocity field is assumed to be the stacking velocity field derived from velocity analysis of the pre-stack data. This step is currently only available for 2D data.

 

Input Links:

1) Seismic data in stacked order (mandatory).

2) Velocity Function cards (optional).

 

Output Links:

1) Seismic data in stacked order (mandatory) and sampled in time.

 

Reference:

Gazdag, J, 1978, Wave-equation migration by phase shift, Geophysics, v. 43, p. 1342-1351.

 

 

Example Flowchart:


 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Migration velocity function: Specify type of velocity to be used for the migration.

 

Use velocity function from data file — If checked, velocity function is defined from an auxiliary velocity card data file.

 

Use average velocity function — If selected, use average of the velocity field defined in the velocity card data file.

 

Select velocity function — If selected, use a velocity function as defined in a specific location from the input velocity card data.

 

Line number — Enter line number for the location of the velocity function.

 

Location number — Enter location number for the location of the velocity function.

 

Use constant velocity — If checked, a constant velocity value will be used as the migration velocity if no velocity cards are linked.

 

Constant migration velocity — Enter constant velocity value to be used for migration.

 

Scale input velocities by — The input velocities are multiplied by this number. This scalar is used for adjusting the input velocities if they are interval velocities derived using Dix's equation rather than true interval velocities.

 

Lenth of taper (traces) — Enter the length of the taper to be used for the migration in number of traces.

 

Specify trace spacing — If checked, overwrite trace spacing by defined value.

 

                True trace spacing (m or ft) — Enter trace spacing in ft or m to overwrite geometry.

 

Remute to first non-zero stack sample — If checked, mute for all traces individually all samples before non-zero.

 

Post-Stack Kirchhoff Time Migration

 

Usage:

The Post-Stack Kirchhoff Time Migration step implements a diffraction summation migration of the Kirchhoff type on a post-stack section, which is capable of handing vertically and laterally varying velocity fields.  The input velocity field is assumed to be the stacking velocity field derived from velocity analysis of the pre-stack data.

 

Input Links:

Stacked seismic data (mandatory).

 

Auxiliary dataset:

Velocity Function cards (mandatory).

 

Output Links:

Seismic file where the migrated section will be saved (mandatory).

 

Reference:

Schneider, W. A., 1976, Integral formulation for migration in two and three dimensions, Geophysics, 43, p. 49-76.

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Migration operator dip limits: Specify if any dip limit will be used for the migration.

 

Limit Operator Dip — If checked, limts the dip angle to be migrated.

 

Dip limit (degrees) — Enter the dip angle of the migration operator.

 

Migration operator anti-alias filter: Specify operator of the anti-alias filter to be applied during the migration.

 

Apply anti-alias function — If checked, apply an anti-aliasing measure to the migration operator.

 

Migration output range: Specify output range of the migrated data.

 

Migrate zero samples — If checked, samples with amplitudes value zero will be migrated as well.

 

Line (Min/Max) — If checked, allows you to limit the range of the migrated CMP lines.

 

Location (Min/Max) — If checked, allows you to limit the range of the migrated CMP locations.

 

Migration operator amplitude correction: Specify how migrated amplitudes are handled.

 

Apply directivity correction — If checked, applies directivity correction to the amplitudes of the migrated data.

 

Apply spreading correction — If checked, applies spreading correction to the amplitudes of the migrated data.

 

Migration velocity field: Specify velocity model used for migration.

 

Use velocity field from data file — If cheked, connect a velocity function to the migration step as input migration RMS velocities.

 

Use constant velocity — If checked, uses a constant velocity model for migration.

 

                Constant migration velocity — Enter the constant velocity value to be used for migration.

 

Apply residual migration — not yet implemented.

 

                Initial migration velocity — not yet implemented.

 

Scale velocity input — Enter a scaling factor for the input velocities, or else 1.

 

Migration input range: Specify input range of the data for the migration.

 

Limit input times (ms) — If checked, input data is limited by time windows.

 

Use constant start time — If selected, defines a constant migration start time.

               

Constant start time (ms) — Enter migration start time.

 

Start time reference to horizon — not yet implemented.

               

                Horizont time multiplier — not yet implemented.

 

Trace geometry: Specify trace spacing.

 

Specify trace geometry — If checked, specifies trace spacing in meters.

               

                Trace spacing — Enter trace spacing in m or ft.

 

Pre-Stack Kirchhoff Depth Migration

 

Usage:

The Pre-Stack Kirchhoff Depth Migration step implements a diffraction summation migration

of the Kirchhoff type on a pre-stack shot gathers. As opposed to the time version, the

depth implementation of the Kirchhoff migration does not compute travel time with a

strait ray propagation assumption. Instead, it uses travel-time tables that were precomputed

using methods like the 2D Paraxial Ray Tracing or the 3D Finite Difference

wavefront tracing. This method handles more accurately vertical and lateral changes in

the velocity fields and dipping reflectors. This implementation is designed to run in single

thread or in parallel, giving it the possibility to take full advantage of multiple processors

at the same time.

 

Input Links:

1)      Pre-Stack seismic data in shot gather order (mandatory).

2)      Source travel-time tables (mandatory).

3)      Receiver travel-time tables (mandatory).

 

Output Links:

1)      Seismic file where the migrated seismic data will be saved (mandatory).

 

References:

-

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Input Dataset: Specify if the input data is from a streamer/land acquisition or OBS recording.

 

Migration limits: Specify spatial extent of data to be migrated.

 

Migrate zero samples — If checked, samples with amplitudes value zero will be migrated as well.

 

Limit operator dip — Ifchecked, limits the dip angle of the migration operator. Enter dip limit in degrees.

 

Minimum offset (m) — If checked, enter the minimum offset for the migration operator.

 

Maximum offset (m) — If checked, enter the maximum offset for the migration operator.

 

Anti-alias filtering and Amplitude correction: Specify if an anti-alias filter is applied to the migration operator and how amplitude will be handled.

 

True amplitude — If checked, uses a weight function to approximate true amplitude.

 

Apply anti-alias filtering — If checked. applies an anti-aliasing measure to the migration operator.

 

Migration grid parameters: Specify migration grid parameters.

 

Starting depth point — Enter the first depth point to be migrated in meters.

 

Depth increment — Enter the depth increment of the migration in meters.

 

Maximum depth — Enter the last depth point to be migrated in meters.

 

Pre-Stack Kirchhoff Time Migration

 

Usage:

The Pre-Stack Kirchhoff Time Migration step implements a diffraction summation migration of the Kirchhoff type on a pre-stack shot gathers, which is capable of handing vertically and laterally varying velocity fields and deals with the energy smear caused by dipping reflectors. The input velocity field is assumed to be the RMS velocity derived from either the conventional velocity analysis (Semblance/CVS) or from the migration velocity analysis tool. This implementation is designed to run in single thread or in parallel, giving it the possibility to take full advantage of multiple processors at the same time.

 

Input Links:

4)      Pre-Stack seismic data in shot gather order (mandatory).

5)      Velocity model or velocity function cards (mandatory).

 

Output Links:

1)      Seismic file where the migrated seismic data will be saved (mandatory).

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

Input Dataset: Specify if the input data is from a streamer/land acquisition or OBS

Dataset type — Select type of data to be migrated (Not yet implemented).

 

Migration limits: Specify limits of the migration.

 

Migrate zero samples — If checked, samples with amplitudes value zero will be migrated as well.

 

Constant Start time (ms) — If checked, defines a constant migration start time.

 

Constant end time (ms) — If checked, defines a constant migration end time.

 

Limit operator dip — If checked, limits the dip angle of the migration operator.

 

Minimum offset (m) — If checked, defines a minimum offset for the migration operator.

 

Maximum offset (m) — If checked, defines a maximum offset for the migration operator.

 

Amplitude correction: Specifies how amplitudes are handled during migration.

 

True amplitude — if checked to use a weight function to approximate true amplitude.

 

High order amplitude function — (Not yet implemented).

 

Migration velocity field: Specify velocity field to be used by the migration.

 

Use velocity from velocity-field file — If selected, connects an auxiliary velocity-field file as input velocity model.

 

Use velocity from card data file — If selected, connects an auxiliary velocity function card as input velocity model.

 

Use constant velocity — If selected, uses a constant velocity migration.

               

                Constant migration velocity — Enter constant velocity value for migration.

 

Scale velocity input — enter a scaling factor for the input velocities, or else 1.

 

Migration operator anti-alias filter: Specifies anti-alias filter parameters.

 

Apply anti-alias function — If checked, applies an anti-aliasing measure to the migration operator.

 

Traveltime calculations: Specify how traveltimes for Kirchhoff migration are calculated.

 

Assuming a flat topography scenario — If selected, assume a flat recording surface when computing travel-time information.

 

Accounting for rugged topography — If selected, Assume a rugged recording surface when computing travel-time information.

 

High order travel-time calculation — (Not yet implemented).

 

 

Stolt Migration

2-D only

Usage:

The Stolt Migration step implements a constant velocity or depth variable Stolt migration algorithm for post-stack time migration. This migration scheme can accommodate a vertically varying velocity field in the form of one SPW velocity function card. This velocity field is assumed to be the stacking velocity field derived from velocity analysis of the pre-stack data.  The user designates a Stolt stretch factor, a maximum frequency to migrate, and temporal and spatial tapers.   An option allows the input velocity function to be scaled.  Finally, you can override the SPW calculated trace spacing and specify the true trace spacing of your data in your spatial units of choice.  By default, SPW calculates the trace spacing for the stack as the group interval, as you defined it in the geometry definition, divided by two (2).

 

Input Links:

1) Seismic data in stacked order (mandatory).

2) Velocity Function cards (optional).

 

Output Links:

1) Seismic data in stacked order (mandatory) and sampled in time.

 

Reference:

Stolt, R.H, 1978, Migration by Fourier transform, Geophysics, v. 43, no 1., p. 23-48.

 

 

Example Flowchart:

 

 

Step Parameter Dialog:

 

 

Parameter Description:

 

Migration velocity function: Specify velocity model parameters for migration.

 

Use velocity unction from data file — If selected, migrates data with a velocity field defined in an auxiliary velocity card data.