NAME
horvel - automatic horizon velocity picking/editting with
velocity tape output
SYNOPSIS
horvel [ -Nntap ] [ -Ootap ] [ -Fftap ] [ -Pstkpik ] [
-vvelpik ] [ -guide ] [ -vgvgate ] [ -Qqtap ] [ -qptap ] [
-snord ] [ -eiend ] [ -pnext ] [ -gigate ] [ -llog ] [ -tthr
] [ -wdepwrd ] [ -vsvmin ] [ -vevmax ] [ -gamma ] [ -X ] [
-E ] [ -I ] [ -R ] [ -V ] [ -? ]
DESCRIPTION
horvel ultimately outputs a velocity tape data set with one
trace (record) per CDP location. It operates in two modes:
(1) an automatic mode (run first) and (2) subsequent edit
modes that uses files generated by the first run.
Mode 1 combines picked horizons from a stacked section, a
velocity fairway, and semblance spectra at fairly dense CDP
coverage (from velspec) to automatically pick the semblance
spectra and output the velocity trace at each CDP by
linearly interpolating the picks made at the available sem-
blances. This mode also optionally outputs a type of QC
semblance data set and an xsd pick file. The semblance data
set is comprised of semblance strips for each horizon. The
traces of each strip are a cut of the semblance spectrum
from the lowest velocity of the scan to the highest. There
will be one trace for every CDP location although only the
velspec control locations will be live. The composite data
set is formed by placing these strips one on top of the
other going from the shallowest horizon to the deepest.
This composite data set can be plotted (e.g. xsd). The
strip boundaries will be obvious since since the lowest and
highest velocites of each is set to -1 and the real sem-
blances will all be positive. The other optional data set
will be a set of picks corresponding to the velocities gen-
erated by the automatic picker and keyed to the horizons.
Mode 2 takes the QC semblance output plotted in xsd or
xmplot and allows the user to load the pick file. For each
horizon the user can then check to see if the automatic
picks truly correspond to legitimate semblance maxima. The
pick segments can be editted and picks moved or even added
and the corrected pick segments saved. When horvel is run
in edit mode the corrected picks are read and used to gen-
erate a new velocity tape.
In auto mode the stack picked horizons are used for each
semblance spectrum to restrict the automatic picker to a
single time, rather than have it wander all over the spec-
trum. Lateral (velocity) wandering is further restricted
either by a fairway (generated by picking two RMS velocity
curves on one of the semblance spectra or on a vertical
stack of all available spectra, or by a velocity gate around
a guide function defined by an input velocity tape. For
each horizon the picker chooses an initial semblance peak
and checks to see if there is a velocity inversion. If so
another semblance peak (along the same curve but at a higher
velocity) is chosen, and so on up to a specified number of
trials, each cycle checking for velocity inversion. If no
legitimate peak (velocity) is found that horizon is bypassed
for that CDP and the user notified in the printout file. In
the case of no horizons producing a velocity for that loca-
tion a simple average of the fairway velocities for that
horizon is currently used to fill out a velocity trace. Any
big boo-boos can fixed in the edit mode.
Between control points where velspec has been run the velo-
cities are interpolated so it's a good idea in areas of
structure that you run as many velspecs as you can stand.
The semblance control points must be keyed to the sequential
record number along the line which demands that the data be
renumbered so that the record numbers start from 1 and
increment by 1 (i.e. by running editt ... -U on the data
before you start running spectra, etc). Velocities will be
linearly interpolated between control points and the func-
tions that come out of the automatic picker will be written
to the printout file.
The output from horvel is a velocity tape with each trace
being a 1 trace record. The number of output records will
be exactly equal to the number of records in the stack pick
file (which means the horizon picks must be made on a stack
section that is itself composed of single trace reords).
Currently horizon picks on the stacked data must go all the
way across the section for each horizon (even if you have to
fake some of them). Any problems caused by this can be
fixed in the edit mode.
horvel can be used to automatically pick residual NMO on 2D
data (for 3D see horvel3d). In this case the semblances must
have been generated using rnmospec. The functions kicked out
by horvel will be gamma values (see rnmospec documentation)
vs time. vomit can then be used to produce a gamma data set
(analog of the normal velocity data set) that can then be
used by rnmo to correct the partially NMO corrected CDPs.
When using rnmo to correct the gathers be sure to use the
proper scale factor (reported in the printout files of
rnmospec and horvel) by using utop -h0T_Unit=[iscl] either
in place on the gamma data set on disk or in the gamma data
stream (iscl is the scale factor, usually 1000).
horvel gets both its data and its parameters from command
line arguments. The picks are in named files created by
xsd.
Command line arguments
-N ntap
Enter the input semblance set name or file immediately
after typing -N unless the input is from a pipe in
which case the -N entry must be omitted. This input
file should include the complete path name if the file
resides in a different directory. Example
-N/b/vsp/dummy tells the program to look for file
'dummy' in directory '/b/vsp'.
-O otap
Enter the output velocity tape data set name or file
immediately after typing -O. This output file is not
required when piping the output to another process.
The output data set also requires the full path name
(see above).
-F ftap
Enter the optional output velocity flat file. It nor-
mally has the format 2-way time, velocity, record
number with function terminated by a negative time. If
the optional header word below is specified then the
output extends to 5 columns with the last two being the
maximum semblance picked followed by the value of the
header word. This extended format not available when
running the code in QC mode (since the input semblances
are not read with the exception of the first record to
extract header information). Default is no output
file.
-P stkpik
Enter the file name containing the horizon picks made
on the stack section. Save the picks with the correct
input sample interval. Horizons do not have to go all
the way across the section but some systematics in your
picking can make life easier: pick the shallowest seg-
ments first working your way left to right; then begin
working your way deeper, again picking segments left to
right. This will make interpreting the QC plot and its
pick segments easier since the semblance strips will
roughly correspond to the stack horizons.
-v velpik
Mode (1): enter the file name containing the fairway
picks. These consist of 2 picks made on a semblance
spectrum (again left to right, top to bottom) which
represent the lowest and highest RMS velocity-time
functions allowed, i.e. the picker will not be allowed
to look beyond these limits at each time horizon. When
saving the xsd picks put the velocity increment in the
"trace units" field and in the "trace offset" field put
in the velocity of the first trace (vmin in the velspec
run) - the velocity increment, e.g. if the increment
was 100m/s and the first trace of the semblance spec-
trum was 1000m/s then 100 goes in the units field and
900 goes in the offset field. Currently not used in
gamma mode. Mode (2): enter the file name of the velo-
city tape data set to be used as guide functions. There
must be a velocity trace for each input semblance
gather.
-vg vgate
For Mode (2) above enter the percent of the velocity at
any given time added to or subtracted from the velocity
guide function to define the semblance search fairway.
Default = 10%
-Q qtap
For automatic mode enter the optional file name for the
output semblance QC data set (comprised of a semblance
strip for each horizon). The data set will be output
as one record having the same number of traces as there
are CDP locations. The number of samples is computed
by multiplying the number of velocities in each sem-
blance scan (from velspec) times the number of horizons
picked on the stack section. The sample interval is
arbitrarily set to 1. It is not necessary to include
this entry on the command line when running in edit/QC
mode, i.e. the second (or more) pass of horvel.
-q ptap
Enter the optional file name for the output pick file.
These picks are in xsd pick format, one segment for
each horizon, and correspond to the velocities gen-
erated by the automatic picker. When saving these
picks besure all units are set to 1. One is not lim-
ited to simply editting the picks generated by the
automatic mode; you can simply pick entirely new tracks
across the semblance strips for each horizon and use
the new picks in a subsequent edit mode run.
-s nord
For automatic mode enter the order of smoothing of the
semblance curves. Default = 5
-l log
For automatic mode enter the sequential record number
increment to output the semblance curves between the
fairway for all horizons. Obviously only the control
semblance analysis points are referred to here. If you
have say 4 analysis locations along a line and you want
to generate curves for all of them then set log to 1.
The curves are output to stderr so the horvel command
line should have >& at the end of it and just before
the name of the file to store the curves. The curves
may then be plotted using xgraph. (See example below).
Default is no curve output.
-g igate
For automatic mode enter the number of samples (in
time) in the semblance gate. This is the number of
isotime semblance curves that are stacked together for
each event before the resulting semblance curve is
searched for peaks. Default = 8 samples.
-t thr
For automatic mode enter the semblance threshold. Sem-
blance values below this limit will be ignored. Default
= 0.1
-w depwrd
For automatic mode enter the optional trace header
value to be written into the flat file output. Specify-
ing this word will extend the output format to include
5 columns: time velocity rec# max_semblance hdr_value.
Default for flat file output is standard 3-cols.
-p next
For automatic mode enter the number of semblance peaks
to test at each horizon. If a velocity inversion is
found for a peak then the program searches the semblace
curve for a peak at a higher velocity (but lower sem-
blance value). Default = 3
-vs vmin
Enter optional minimum velocity to peg the zero time of
each trace. This will have no effect on the picking,
only on the output velocity tape. This is useful when
the shallow semblances too ratty to pick consistently
causing these horizons to be skipped. This causes the
deeper velocities to propagate into the shallow parts
of the section leaving vertical high velocity stripes
in the output velocity tape. Pinning the start velocity
minimizes this problem. Default is to ignore this
option.
-ve vmax
Enter optional maximum velocity to peg the end time of
each trace. This will have no effect on the picking,
only on the output velocity tape. This is useful when
the semblances become too ratty to pick for the deeper
horizons and these horizons keep being skipped. This
causes the shallow velocities to propagate deep into
the section leaving vertical lower velocity stripes in
the output velocity tape. Pinning the end velocity
minimizes this problem. Default is to ignore this
option.
-gamma
Enter the command line argument '-gamma' if the input
semblances are gamma-T scans rather than X-T scans.
Gamma scans use the NMO residual correction formula:
sqrt [ t0 **2 + (gamma **2 - 1) * (offset/2) **2 ],
where t0 is the zero offset time or depth.
-X Enter the command line argument '-X' if the optional
output velocity function file is to be xsd format, else
the format is flat file (time velocity rec).
-E Enter the command line argument '-E' to run horvel in
edit/QC mode. This will always be a subsequent run,
never a first run (i.e. the automatic mode must be run
first).
-I For edit/QC mode enter the command line argument '-I'
to turn off the pick interpolator. The default state
is to do linear interpolation between QC picks.
-R Enter the command line argument '-R' to use the fairway
average velocity for those semblance records that can-
not be picked; otherwise ignore those records and
interpolate velocities from those records that contain
valid picks. Turing this on will only affect the first
(non QC) output velocity tape not the the pick file.
-V Enter the command line argument '-V' to get additional
printout.
-? Enter the command line argument '-?' to get online
help. The program terminates after the help screen is
printed.
BUGS
No automatic picker is foolproof. Failure to provide a
tight fairway or sloppiness in picking horizons on the
stacked section will result in bad velocities even given
sophisticated logic to determine bad initial picks. For
fairway picking it's a good idea to take all the velspec
spectra and vertically stack them ( rstak -nnrec, where nrec
is the total number of spectra in the data set. This shows
the velocity limits overall better than looking at a few
individual spectra.
SAMPLE COMMAND LINE
1) automatic mode only
horvel -Nspectra -Pstackpiks -vfwaypiks -Ovtape -l50 >&
curve
This generates a velocity tape, vtape, and a set of sem-
blance curves for the horizons of sequential record 50 and
store these in the file curve.
xgraph < curve
This plots the curves.
2) auto/edit mode
horvel -Nspectra -Pstackpiks -vfwaypiks -Ovtape -Qqtap
-qptap
which genrates the initial velocity tape in the automatic
mode. The semblance strips are in the qtap data set and the
xsd picks are in the file ptap.
horvel -Nspectra -Pstackpiks -vfwaypiks -Ovtape1 -qptap1
which uses ptap1, the result of editting the original picks
ptap and outputs a new velocity tape, vtape1.
SEE ALSO
velspec
AUTHOR
Paul Gutowski, APR, Ron Scheet, Houston, and Norm Kohlham-
mer, Calgary
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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