NAME
opstcv - resamples the constant Tp semblance traces output
by program OPSTF into constant velocity traces for analysis
SYNOPSIS
opstcv [ -Nntap ] [ -Ootap ] [ -pkpkfile ] [ -rsnrst ] [
-renred ] [ -vmvmin ] [ -vxvmax ] [ -W ] [ -F ] [ -? ]
DESCRIPTION
opstcv resamples the constant Tp semblance traces output by
program OPSTF into constant velocity traces for analysis.
Resampling the semblance data like this permits evaluation
both of the optical stack process and the data in a more
conventional manner, since the constant velocity semblance
traces output are now in the form of the conventional velo-
city spectrum. This data may be viewed by any display pro-
cedure but is most efficiently viewed and analyzed by the
optical stack analysis program XOS.
This program is one of six programs in a suite of programs
for creating, processing, and/or analyzing optical stack
results. The other programs in the suite, and their func-
tions, are:
opstf - create forward Tp scans and semblance panels
opstk - Extracts the stack and the velocity field from the
optical stack panels.
opstd - Demultiplexes the OPSTF output to create separate
optical stack and semblance panels for analysis and applica-
tion of muting using polymute.
opstr - create reverse of opstf
XOS - Provides graphical analysis of optical stack or
semblance panels created by OPSTF.
Command line arguments
-N ntap
Enter the input data set name or file immediately after
typing -N unless the input
is from a pipe in which case the -N entry must be
omitted. The input to the optical stack to conven-
tional velocity conversion program OPSTCV is the sem-
blance panels created by program OPSTF. Because the
OPSTF output contains both Tp scan and semblance data,
in multiplexed format, the input to program OPSTCV must
be extracted from OPSTF output with program OPSTD.
polymute should be run on the semblance data (picked at
control records along the line) to better isolate the
primary wraps from the multiples.
-O otap
Enter the output data set name or file immediately
after typing -O. This output file is not required when
piping the output to another process. The output from
program OPSTCV contains semblance data in trace format,
where each trace represents the point-wise semblance
for a user-defined stacking velocity. These semblance
traces are the same as those which would have be
obtained with conventional velocity analysis.
-pk pkfile
Name of the ASCII file containing XSD- and XOS-
compatible picks extracted from the semblance data.
Values in the 3rd column of the file are in velocity.
Default: No pick file output.
-vm vmin
Enter the slowest stacking velocity, in ft/sec or
m/sec, for which a semblance trace is desired. The
value supplied here should be represented in the Tp
semblance panels. If not, a a zero-valued trace is
output. The units of this value must agree with those
of the initial velocity used in OPSTF. Default: None.
This parameter is required.
-vx vmax
Enter the fastest stacking velocity, in ft/sec or
m/sec, for which a semblance trace is desired. The
value supplied here should be represented in the Tp
semblance panels. If not, a a zero-valued trace is
output. The units of this value must agree with those
of the initial velocity used in OPSTF. Command Line
Mnemonic: -vx Enter maximum velocity to use in data.
Default is maximum available.
-nv nvel
Enter the number of constant velocity traces to output
for each input semblance panel. This parameter deter-
mines the velocity increment between the traces.
Default: None. This parameter is required.
-th thresh
Enter the smallest semblance value to be considered in
picking of the semblance data. The value of this
parameter must be between 0.0 and 1.0. Default: 0.35.
-rs nrst
Enter start record number. Default value is the first
record.
-re nred
Enter end record number. Default value is last record.
-W If present weight stack with semblance
-F If present apply spatial DC (flat dip) filter
-? Enter the command line argument '-?' to get online
help. The program terminates after the help screen is
printed.
DISCUSSION
Operations
Resampling procedures
The semblance data output by program OPSTF is in the form
panels containing one semblance trace for each Tp included
in the analysis, with one panel for each CDP analyzed.
These traces represent the semblance obtained when the CDP
gathers were corrected for normal moveout according to the
optical stack moveout equation. Although these panels have
the same appearance as conventional velocity spectra, the
semblance data is sampled in Tp, not in velocity as in con-
ventional velocity analysis. The equation
Vs = V0*SQRT(Tp/T0),
however, gives the relationship between stacking velocities
Vs and Tp (in this equation, V0 is the intial velocity
required by OPSTF, T0 is zero-offset time, and "SQRT" means
square root). This equation can be used to find a Tp for a
given, constant velocity for all time and to permit the
resampling of the Tp ordered semblance data to constant
velocity ordered semblance data.
To accomplish the resampling, the user supplies a minimum
and maximum velocity for which semblance traces are desired
and the total number of traces desired. The above equation
is used to find the Tp corresponding to each of the veloci-
ties, for each time sample. The semblance data correspond-
ing to each Tp and each sample is extracted from the input
semblance panel, with cubic spline interpolation between
fractional Tp's. The trace thus generated is the semblance
trace which would have been created for the given velocity
by conventional velocity analysis procedures.
Mute Application
A mute function should be applied to the semblance panels
before input to opstcv using polymute. This mute may be
used to attenuate undesirable events, such as multiple
reflections, in the semblance data. The mute functions can
be created in xsd by picking polygon mute zones on control
records along the line. polymute will smoothly morph between
control points.
Pick File
If a pick file is requested, the constant velocity spectra
are automatically picked and the results saved as an ASCII
file. This file contains the record, trace, and time coor-
dinates of each of the picks and may be displayed as over-
lays on the spectra in the optical stack analysis program
XOS.
The picking method use is one frequently used in conven-
tional velocity analysis. In this method, an envelope of
semblance maxima is assembled from a semblance by scanning
for groupings of maxima which meet or exceed a user-defined
threshold limit. The maxima in this envelope then define
the location (trace, or velocity, and time) of greatest sem-
blance and thus the appropriate stacking velocity for the
identified time sample.
REFERENCES
de Bazelarie, E., 1988, Normal moveout revisited: Inhomo-
geneous media and curved interfaces, Geophysics, Vol. 53,
143-157.
Arnold, Richard H. and Semaan, Mars E., 1990, Implementation
of the Optical Stack Method, SEG Expanded Abstracts, Vol II,
San Francisco.
BUGS
internal muting has been removed in favor of the more flexi-
ble polygonal (external) mute.
SEE ALSO
opstr, opstk, opstd, opstf
AUTHOR
Richard Crider, ES&S
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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