Navigation lines, shot point numbers and stacking velocities
Introduction
The Navigation plug-in Geocap handles seismic navigation lines, stacking velocities and depth conversion. The plug-in is part of the Oil & Gas module.
The following describes the command syntax for the functionality collected in this plug-in.
Together with general mapping and modeling functionality in Geocap it governs a flexible platform for velocity analysis and horizon based depth conversion.
The functionality can be operated through scripts, commands or a user dedicated menu.
On this page:
Description of navigation lines, shot point numbers and stacking velocities
Navigation lines are also called stacking velocities or shot point lines and will be used interchangeably.
The navigation lines go in one direction. Each navigation line contains many different shot point numbers.
Shot points of same number go in the other direction. Underneath each shot point sits the stacking velocities in a gather.
Shot points and navigation lines
Detail of navigation lines and id and some shot point numbers
Navigation stacking velocities.
The following ASCII shot point file represents an example:
Line name Shot point x coord y coord time velocity
3359I 1280 530196.6 6757992.7 548 1517
3359I 1280 530196.6 6757992.7 608 1566
3359I 1280 530196.6 6757992.7 664 1585
. . . . . . . . .
. . . . . . . . .
3359I 1280 530196.6 6757992.7 3774 3318
3359I 1280 530196.6 6757992.7 4014 3464
3359I 1280 530196.6 6757992.7 4986 3961
3359I 1320 530064.0 6758475.0 0 1470
3359I 1320 530064.0 6758475.0 475 1470
3359I 1320 530064.0 6758475.0 562 1533
3359I 1320 530064.0 6758475.0 615 1573
. . . . . . . . .
. . . . . . . . .
3439I 1280 531160.9 6758258.8 0 1470
3439I 1280 531160.9 6758258.8 472 1470
3439I 1280 531160.9 6758258.8 519 1476
3439I 1280 531160.9 6758258.8 587 1525
. . . . . . . . .
. . . . . . . . .
This special format is called a navigation velocity stacking format in Geocap and the whole file is converted to a Geocap vtk file and placed in the project.
This file is read into a project folder by Import->Stacking Velocities. Shot point are in field data SP and Line Name are in field data 2Dline.
Check the import afterwards in Table View to see that the field data columns are properly assigned.
The navigation file is converted to a cell structure making a new cell whenever the shot point number changes.
The command syntax for manipulation this dataset is placed under the command nav for navigation, because this kind of file traditionally belongs to a navigation file.
All functionality connected to the nav command is placed in the plug-in called Navigation. This plug-in is included in the Oil & Gas module and must be loaded into Geocap in order to operate the functionality.
Syntax description of the nav command.
Making new datasets from the navigation stacking file
The following commands require that the stacking velocity dataset is the active data.
nav mak cells ;# make cells of stacking velocity. Each vertical stacking column is a cell. Should be performed if the stacking velocity file has no cell structure; i.e. contains only one cell.
nav mak shotpoints ;# make one line set of all the first top shot points.
nav mak timevel selshot cur | _shotpoint_number ;# select time and velocity data for shot point closest to the cursor position (cur) or for a certain shot point number shotpoint_number. Produces also an additional dataset navcross in workspace which can be triangulated by nav gen trg.
nav mak timevel cur ;# make time and velocity column at the cursor position.
Making navigation stacking file from SEGY dataset.
The situation is that stacking velocities are present as a SEGY file which is read into a seismic folder as usual. The task is to convert the stacking velocities in the seismic format to the standard stacking velocity format.
The following command require that the outline is in workspace outline and the amplitude grid in the SEGY file is in active.
nav lin [resolution_in_xresolution_in_z] [xstart x zstart z] [name SEGY_file_name ]
resolution_in_x
The sample resolution in x direction is resolution_in_x value. Similar for depth or z direction.
xstart x
Specifies where to start the sampling in x direction. Similar in z direction.
name SEGY_file_name
Specifies the name in the field data 2Dline. This should normally be the name of the SEGY dataset.
Example of converting SEGY stacking velocity format to standard navigation stacking velocity format
nav lin ;# makes vertical lines for all nodes (grid in active, outline in outline)
nav lin 1 4 ;# makes vertical lines of sample 1 in length direction (x) and 4 in depth (z).
# The result is placed in workspace seislines.
Displaying data directly from the navigation stacking file.
The following commands require that the stacking velocity dataset is the active data.
Generating a dataset by cutting at z-level in the navigation stacking file.
The following commands require that the stacking velocity dataset is the active data.
Generation of triangle dataset from the selected line velocity stack.
The following command require that the selected velocity stack along a line is active data.
An alternative is to run a prestep that makes an equal number of points for adjacent shot point gathers. This option is safer because it may work with a high resolution in all cases.
After this command one gets a solid vertical section that can be mapped and contoured.
Generation of velocity cube from the navigation stacking file.
The stacking velocities are active data.
Setting an id that can subsequently be used by other nav commands.
nav set hicoreid – sets an id that can be used in other nav commands.
It can work like this:
set job <something>
nav set hicoreid $job
and then, later on
nav cal dix stack will need the following data sets to be present in workspace:
topTimeVelocity$job
bottonTimeVelocity$job
topTimeSurface$job
bottonTimeSurface$job
This is a common feature in all nav commands which use hicore (workspace).
Preset hicore names that can be adjusted by a hicoreid
topTimeSurface
topTimeVelocity
topTimeVelocityStack
bottomTimeSurface
bottomTimeVelocity
bottomTimeVelocityStack
stackingVelocityData
stackingVelocityCube
intervalVelocityDix
intervalVelocityStackDix
highSurface
Adjusting the velocity cube to check shot wells.
The velocity cube is active data.