NAME
ivad - Create a V(x,z) Velocity Field by interpolating velo-
cities along dip
SYNOPSIS (1)
ivad [-N intape] [-O outtape] [-I vfunctions] [-P ich] [-V]
[-h] [-?] [-ND mindip] [-XD maxdip] [-ID incdip] [-B ibox]
[-M imed] [-T thresh] [-S nsemb] [-TM time] [-D type] [-DZ
dz] [-Z depth] [-DX dx] [-X width] [-NF nfunc] [-u iunder]
[-ixf ixf] [-ixb ixb]
SYNOPSIS (2)
ivad -N[intape] -O[outtape] -I[vfunctions] -P[ich] -ixf[ixf] -ixb[ixb] \
-u[iunder] -ivad.crd"\
SPIN MINDIP MAXDIP INCDIP IBOX IMED THRESH NSEMB TIME TYPE
mindip maxdip incdip ibox imed thresh nsemb time type
SIZE DZ TDEPTH DX TWIDTH NFUNC
dz tdepth dx twidth nfunc
"
#...|....1....|....2....|....3....|....4....|....5....|....6....|
STARTJOB
Program ivad may be run using command line arguments like
Synopsis (1) above.
- OR -
Create a file that looks like Synopsis (2) above with the
following command:
catpat ivad > ivad.job
The ivad.job file will have some default parameter values
entered. Edit the job to suit your needs and submit
ivad.job with the following command:
startjob ivad.job
DESCRIPTION
ivad creates a velocity dataset by interpolating interval
velocities along dip of a seismic time or depth section.
Ivad computes a dip for every sample by correlating traces
in a window.
The input seismic data can be in either time or depth, but
the velocity cards are always input as depth/interval velo-
city pairs. If the input seismic is in time, ivad will
internally convert the depth/interval velocity pairs pro-
vided on the velocity cards to time/interval velocity pairs.
Most commonly, the output is the velocity field, but alter-
native outputs are semblance, dip, or median dip.
The input velocity cards must be in a vlmx-compatible for-
mat. The velocities in the card deck are referenced to the
bottom of the layer defined by the corresponding depth.
Optionally, faults can be defined for disrupting the inter-
polation (i.e., velocities will not be interpolated across a
fault).
Command line arguments
-N intape
Enter the input dataset name (depth or time migrated
seismic section) after typing -N.
-O outtape
Enter the output dataset name of the velocity field
after typing -O.
-I vfunctions
Enter the name of the file containing the interval
velocity functions after typing -I. The card file for-
mat is shown below.
-P ich
Enter the name of the ich input dataset which contains
the faults. The ich dataset must be in depth if the TM
parameter is 0. Otherwise; the ich dataset must be in
time. When running ich, the S option must be used to
output spikes instead of wavelets. For information on
program ich, see the man pages. By default, no faults
are used.
-V Enter -V for a verbose printout.
-h Enter -h for online help. Program will terminate after
printing this.
-? Enter this (or '-?' if you are running in c-shell) to
get online help. The program will terminate after
printing this.
-ivad.crd"\
When using Synopsis (2) shown above, this keyword,
-ivad.crd"\, must be entered exactly as shown with no
spaces after the backslash. The embedded menu cards
that follow this keyword must be typed exactly as
shown, with the lower case parameter names being
changed to the actual values you want the program to
use. All of the parameter values must be entered in the
correct columns. The double quote following the embed-
ded menu cards must be present as shown.
Description of parameters
-ND mindip
Enter the minimum dip (samples per trace) to use for
the interpolation along dip. By setting both the
minimum and maximum dip parameters to 0, you will get a
velocity field similar to a vlmx velocity field (Actu-
ally the velocity field will be less blocky, as ivad
has a smoother interpolation than vlmx.). If the input
is in time, the output velocity field may not be flat-
layered because the velocity field will be converted
back to depth using the interpolated velocities.
-XD maxdip
Enter the maximum dip (samples per trace) to use for
the interpolation along dip. By setting both the
minimum and maximum dip parameters to 0, you will get a
velocity field similar to a vlmx velocity field (Actu-
ally the velocity field will be less blocky, as ivad
has a smoother interpolation than vlmx.). If the input
is in time, the output velocity field will may not be
flat-layered because the velocity field will be con-
verted back to depth using the interpolated velocities.
-ID incdip
Enter the interval for computing dip (samples per
trace) to use for the interpolation along dip.
Strongly recommended value is 1.
-B ibox
Enter the length (samples) of boxcar semblance
smoother. Recommended value is 21.
-M imed
Enter the length (samples) of median filter for dips.
Recommended value is 41.
-T thresh
Enter the minimum (smoothed) semblance value for non-
zero dip. Recommended value is .1.
-S nsemb
Enter the number of traces to use in semblance scan.
Recommended value is 11.
-TM time
Enter flag to indicate the type of input data:
0 = depth input
1 = time input
-Dtype
Enter the desired output type:
1 = interval velocity (default)
2 = semblance
3 = dip
4 = median dip
-DZ dz
Enter the sample spacing (ft or m) of the output velo-
city field.
-Z depth
Enter the total depth (ft or m) of the output velocity
field.
-DX dx
Enter the trace spacing (ft or m) of the output velo-
city field. It is also the implied record spacing of
the input velocity functions (see xloc parameter for
vfunction card).
-X width
Enter the total width (ft or m). Ivad computes the
total number of output traces by dividing the total
width by the DX value.
-NF nfunc
Enter the number of velocity functions to read from the
"vfunctions" card file.
-u iunder
Indicate how to interpolate beneath short functions
(i.e., those which are not defined to the depths of the
adjacent functions).
0 = do not interpolate beneath short v(z) functions.
Short functions will be extended to the total
depth by repeating the last velocity. Inter-
polation in x will then continue between
functions.
1 = interpolate under short v(z) functions.
Short functions will not be extended to the
total depth and velocities will be interpolated
from adjacent v(z) functions. For example, when
uncertain about the velocities below a salt body,
a velocity function can be input on either side
of the salt body, and one to the bottom of the
salt body. Then the program's interpolation will
extend the known velocities under the salt body
along structure.
-ixf ixf
Indicate whether to use a flat layer extrapolation
after the last velocity function on the line. The
flat-layer extrapolation cuts down on edge effects. The
last velocity function will always be extrapolated to
the end of the line regardless of the value of this
flag. Enter the desired extrapolation type:
0 = extrapolate along dip
1 = flat layer extrapolation
Defaults:
0, if number of velocity functions < 3
1, if number of velocity functions >= 3
-ixb ixb
Indicate whether to use a flat layer extrapolation
before the first velocity function on the line. The
flat-layer extrapolation cuts down on edge effects. The
first velocity function will always be extrapolated
from the first of the line regardless of the value of
this flag. Enter the desired extrapolation type:
0 = extrapolate along dip
1 = flat layer extrapolation
Defaults:
0, if number of velocity functions < 3
1, if number of velocity functions >= 3
VFUNCTIONS CARD FILE FORMAT
MODEL nv xloc
VELOCITIES VINT DEPTH
n1 vel01 dep01
n2 vel02 dep02
. . .
. . .
nv velnv depnv
#...|....1....|....2....|....3....|....4....|....5
description of vfunctions parameters:
-nv nv
Enter the number of velocities that describe the func-
tion for this location.
-xloc xloc
The xloc value is the trace number on the input seismic
dataset where the velocity function should be applied.
The program will assume that the actual physical loca-
tion of the function is xloc*dx.
VELOCITIES n1.....nv
This is an integer value corresponding to the
velocity/depth pair.
VINT vel01.....velnv
These values are the interval velocities (ft/sec or
m/sec) that correspond to the depths (ft or meters).
These values are the depths (ft or meters) that correspond to the
interval velocities (ft/sec or m/sec).
BUGS
No known bugs.
SEE ALSO
mbs, startjob beginjob, endjob, swath, vlmx, xrpm, velin,
rmsvlmx, mxcvel, vfnd, vtpad, vtrsiz, vtvzex, vttd
AUTHOR
Gary Murphy
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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