NAME
pwmvzn - Constant Angle Phase Shift Prestack Migration for
V(z)
SYNOPSIS
pwmvzn -Npwtime -Opwdepthvz -VCvelo.cards -Sstretchparm [-TIME] -V \
-pwmvzn.crd"\
TIME ENDTIMEMS PADTIMEMS BEGTIMEMS DTMS
TIME endtime padtime begtime dtms
FREQUENCY MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ
FREQUENCY f1 f2 f3 f4
DEPTH MAX DEPTH DELTA Z
DEPTH zmax dz
WIDTH DELTAX BEG REC END REC REC INC BEGTRACE ENDTRACE
WIDTH dx irbeg irend irinc itrbeg itrend
MODEL REF VELOC BEAMWIDTH PADTRACE
MODEL vref bw ipad
# ANGLES START INCREMENT
nang angstrt anginc
"
#...|....1....|....2....|....3....|....4....|....5....|....6....|....7
STARTJOB
Create a file that looks like the above synopsis with the
following command:
catpat pwmvzn > pwmvzn.job
This pwmvzn.job file will have some suggested parameter
values entered. Edit this file to suit your needs and sub-
mit pwmvzn.job with the following command:
startjob pwmvzn.job
DESCRIPTION
pwmvzn images V(z) constant angle prestack time sections
into depth sections using a fast phase-shift algorithm. The
phase-shift algorithm assumes a flat-layer model, which is
described as a table of sequential velocities and depths.
By appropriately selecting incident and reflected veloci-
ties, the user can optionally elect to perform a migration
of converted-wave data (i.e., P to S or S to P events).
Program parameters are read from the embedded menu file
shown above. Program pwmvzn reads the velocity model from a
filename provided by command line argument or from an embed-
ded file, as given in the catpat example. The input and
output seismic data files are in USP format, and filenames
are provided by command line arguments.
Command line arguments
-N pwtime
Enter the name of the input dataset after typing -N.
This data should be in USP format and should be con-
stant angle plane wave time sections.
-O pwdepthvz
Enter the name of the output dataset after typing -O.
This data will be in USP format and will be constant
angle migrated depth sections.
-VC velo.cards
Enter the name of the file containing the input velo-
city function after typing -VC. This file can be
entered via an embedded structure as given with the
catpat-provided template, or it can be entered as shown
in the format below. Velocity cards are read in with a
fixed format; therefore, entries must be in the correct
columns.
-S stretchparm
Enter the stretch parameter after typing -S. The velo-
city, maxdepth and dz will be multiplied by this
number. Default is 1 (no stretch). This parameter can
be used to test different velocity models which change
by a constant amount. Note that the actual depth spac-
ing will be changed by this parameter.
-TIME
If this flag is present on the command line, the output
will be in TIME rather than in DEPTH. The output time
sample interval will be DTMS, which is described below.
-V Enter -V for a verbose printout.
-pwmvzn.crd"\
This keyword, -pwmvzn.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
embedded menu cards must be present as shown.
Description of Parameters
ENDTIMEMS endtime
This value is in ms and should be less than or equal to
the time on the input dataset. Default is the maximum
time on input.
PADTIMEMS padtime
This value is the amount of time in ms needed to reduce
frequency wraparound. If the requested maximum depth
exceeds the computed maximum depth (computed from
maximum time and velocity structure), the migrated
seismic data will wrap around. This will cause repeats
of the shallower seismic data at those depths which are
undefined by the data. Default is 0.
BEGTIMEMS begtime
This value is in ms and should be 0 or a positive
number. This is used mainly for model data.
Enter the input sample spacing in ms of the input seismic data.
Default is the line header value. If the output is in time, this
value will also be used
for the output sample interval.
MINFREQHZ F2FREQHZ F3FREQHZ MAXFREQHZ f1 f2 f3 f4
The frequency points in a trapezoidal filter in Hz.
MAX DEPTH zmax
The data will be migrated to this maximum depth (ft or
meters). No default.
The output depth spacing in ft or meters. This value should be
less than or equal to
vmin/(maxfreq*4). No default.
The input trace spacing in feet or meters. No default.
BEG REC irbeg
The beginning record to process (as a count from the
beginning of the line) from the input to process.
Default is 1.
END REC irend
The ending record to process. Default is the number of
records specified in the line header.
REC INC irinc
The record increment. Default is 1.
BEGTRACE itrbeg
The trace number of the first trace to process.
Default is 1.
ENDTRACE itrend
The trace number of the last trace to process from the
input. Default is number of traces per record on the
line header.
REF VELOC vref
The reference velocity value for the dip filter. This
value must match the reference velocity value given to
program slnt!
BEAMWIDTH bw
Enter the beamwidth in degrees. The reflected field is
dip filtered around the normal incidence ray where the
angular pass zone is BEAMWIDTH wide. If BEAMWIDTH is
near 0, only normal incidence data will be passed.
Reflections from flat layers with emergent angles
greater than 2*BEAMWIDTH will be attenuated. Recom-
mended value is 90.
PADTRACE ipad
The number of zero traces to pad to reduce spatial wrap
around. Recommended value is 100. No default.
# ANGLES nang
The number of angles on input dataset. MUST MATCH
INPUT.
RT angstrt
The starting angle (in degrees) on input dataset.
INCREMENT anginc
The angle increment (in degrees) on input dataset.
FORMAT OF VELOCITY CARDS
You can use the catpat command to create a template similar
to the one shown below:
MODEL nv
VELOCITIES REFLECTED INCIDENT END DEPTH
1 vr01 vi01 d01
2 vr02 vi02 d02
3 vr03 vi03 d03
4 vr04 vi04 d04
5 vr05 vi05 d05
. . . .
. . . .
. . . .
nv vrnv vinv 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 vr01...vrnv
This value is the reflected velocity (ft/sec or m/sec).
No default.
INCIDENT vi01...vinv
This value is the incident velocity (ft/sec or m/sec).
The reflected velocity and the end depth must be speci-
fied. The incident velocities will default to the
reflected velocities if they are not specified. For
migration of P-SV events, enter P velocity for incident
and S velocity for reflected. Enter the reverse for
SV-P events.
END DEPTH z01...znv
This value is the ending depth (ft or meters) for the
corresponding velocities. The last end depth must >=
MAX DEPTH parameter described above. No default.
SEE ALSO
mbs, startjob, beginjob, endjob, kmpw, fxpwmig
BUGS
None known.
AUTHOR
N. D. Whitmore, Jr., Ron D. Coleman, Mary Ann Thornton
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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