NAME
cmmvz3d - (Step 2 of 3) 3D V(z) Phase Shift Poststack Depth
Migration
SYNOPSIS
[ < input] [out=output] [vel=vel_model] [data_path=path]
[data_suffix=suffix] [zeta_suffix=suffix] [dz=dz] [dtms=dt]
[zmax=zmax] [tmax=tmax] [vref=vref] [maxdip=dip]
[stretch=stretch] [flags=V and C or T] [-?] [-h]
DESCRIPTION
cmmvz3d is the second step of the three step process. Type
catpat 3dvzmig > 3dvzmig.job
for a script which will execute all three steps of the
migration process. cmmvz3d images input data which is in
(w, kx, ky) coordinates into depth data with a fast phase-
shift algorithm. The original time data is typically a CMP
stacked dataset which is the output of fft3d. The phase
shift algorithm assumes a flat-layered model, which is
described as a table of sequential velocities and depths (at
the base of each layer). cmmvz3d gets the input and output
filenames and other parameters from command line arguments
as described below. Both the input and the output datasets
are USP formatted.
Command line arguments
> ntap
Enter the input dataset name after typing > .
out=outfile
Enter the `basename' of the output dataset after typing
out= . This program will produce three files:
`basename`.cmmvz3d which is a dictionary file which
gives basic information about the seismic data;
`basename.cmmvz3d.zet` which is a dictionary file con-
taining information about the phase-shift steps; and
`basename`.cmmvz3d.usp which is a USP formatted
seismic data in coordinates (z, kx, ky).
vel=vel_model
Enter the name of the file containing the input velo-
city function after typing vel= . This file can be
entered via an embedded structure as given with the
catpat provided template for vzcards, or program vtvzex
can be used to extract a velocity function from a 2D or
3D velocity field. Velocity cards are read with a
fixed format, therefore entries must be in the correct
columns.
data_path=path
This specifies the full pathname to the directory where
you want the output to be written. There is no
default.
data_suffix=suffix
This specifies the third part of the name for the
seismic data file described above. The default is
"usp".
zeta_suffix=suffix
This specifies the third part of the name for the
phase-shift dictionary file described above. The
default is "zet".
dz=dz
This value is in feet or meters and represents the sam-
ple spacing increment in depth. The values of dz and
dtms are used to force the boundary between velocities
to an integer multiple of either dz or dt. Thus, dz
and dt cannot both be greater than zero. If both are
less than or equal to zero, then dz is set to the
reference_velocity/200.
dtms=dt
This value is the sample spacing in time. The values of
dz and dtms are used to force the boundary between
velocities to an integer multiple of either dz or dt.
Thus, dz and dt cannot both be greater than zero. If
both are less than or equal to zero, then dz is set to
the reference_velocity/200.
zmax=zmax
This value is in feet or meters and represents the max-
imum depth to migrate.
tmax=tmax
This value is in milliseconds and represents the max-
imum time to use from the input dataset.
vref=vref
This value represents the reference velocity in feet or
meters per second for the dip filter. It will be used
with the maxdip parameter to perform f-k filtering.
There is no default.
maxdip=dip
This value is in degrees, and represents the maximum
dip angle. The default is 90 degrees. The input data is
f-k filtered so that dips are passed between:
-sin(dip)/vref and +sin(dip)/vref
stretch=stretch
This value is a horizontal regridding rate. The
migration will be done at (stretch * dx) and then
interpolated back to dx. This decreases run time by an
amount equal to "stretch". Warning: watch spatial
aliasing! The default value is 1.0.
flags=flags
The choices of flags to be entered after typing flags=
are:
V - This gives verbose printout
C - Compute phase-shift operators (This is the default.)
T - Table look-up the phase-shift operators
-h Enter -h for online help. The program will terminate
after printing this.
-? Enter -? for online help. The program will terminate
after printing this.
FORMAT OF VELOCITY CARDS
The format for the velocity function cards is shown below.
MODEL nv
VELOCITIES REFLECTED END DEPTH
1 v01 d01
2 v02 d02
3 v03 d03
4 v04 d04
5 v05 d05
. . .
. . .
. . .
nv vnv dnv
#...|....1....|....2....|....3....|....4
Description of parameters for Velocity Function Cards
MODEL nv
This value is the number of velocities appearing in the
velocity function.
VELOCITIES n1.....nv
This value is the sequential number of this velocity
layer and must be an integer number. These numbers
must increment by 1.
REFLECTED v01...vnv
This value is the reflected velocity in feet or meters
per second. There is no default.
END DEPTH d01...dnv
This value is the ending depth in feet or meters for
the corresponding velocity. The last END DEPTH must be
greater than or equal to the ZMAX parameter described
above. There is no default.
SEE ALSO
mbs, dspace, 3dvzmig, fft3d, zkk2zxx
BUGS
None known.
AUTHOR
N. D. Whitmore, Jr., Ron D. Coleman
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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