NAME
sempik - semblance auto-picker
SYNOPSIS
sempik [ -Nntap ] [ -Ootap ] [ -Pptap ] [ -Ggtap ] [ -Qqtap
] [ -snord ] [ -gigate ] [ -dudevu ] [ -dldevl ] [ -ppass ]
[ -X ] [ -L ] [ -I ] [ -V ] [ -? ]
DESCRIPTION
sempik takes each input semblance panel and using a user
supplied guide function attempts to pick all semblance wraps
lying within a user defined fairway. The output is a set of
velocity traces, a pick file, and an optional stacked sem-
blance file. Unlike horvel which is restricted to only a few
horizons (although you get to choose them and you can edit
the picks in mode 2) sempik does every horizon as determined
from the semblances themselves. This is a batch process with
no provision for editting the velocity functions.
Each input semblance record is stacked within the fairway
producing a stacked semblance trace (normalized to the
number of samples at each time within the fairway boun-
daries). All peaks (i.e. all horizons) on this trace are
then identified. For each time corresponding to a horizon
the semblance record is searched between the fairway bounds
for a semblance peak and the corresponding velocity is
recorded for that time. Provision is made for looking at a
gate of times about the horizon time and some logic deter-
mines that if the picked velocity lies on a fairway boundary
a secondary or tertiary peak is searched for. After all the
horizons have either been picked or skipped (if no alternate
peaks could be found) the resulting velocity function is
output both as a velocity trace and as a pick file (xsd or
flat file format).
The fairway is defined by picking guide functions on
selected semblances in xsd. The picks are saved making sure
the record units and offset are set to correspond to the
actual record numbers (RecNum) displayed (remember the first
pick record number is computed by adding the units to the
offset). The trace units is filled in with the velocity
increment (this can be determined by keying on the of trace
header items to DstSgn - signed trace distance - which will
clock the velocity for each semblance trace). The trace
offset is set so that trace 1 has the correct velocity.
sempik gets both its data and its parameters from command
line arguments. These arguments specify the input, output
velocity and pick file names, the fairway and search parame-
ters , and verbose printout, if desired.
Command line arguments
-N ntap
Enter the input semblance data set name or file immedi-
ately 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'. There will be an output
for each semblance input record (unless the semblance
record is dead).
-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).
-G gtap
Enter the input xsd pick file defining the guide func-
tion. These picks are made on selected semblance con-
trol records chosen from the complete suite of sem-
blances run (i.e. using velspec). There must be one
segment for a semblance panel but all panels don't have
to be picked. When saving the picks the record and
trace units must be filled out properly since sempik
needs this info (1) to extract the velocities for the
fairway and (2) to know where among the input sem-
blances the guide functions occur. The guide functions
are linearly interpolated between semblance records
that have not been picked. This command line input must
be supplied.
-P ptap
Enter the output pick file name. This will contain
velocity-time functions for the horizons found for each
input semblance record (unlike the velocity trace out-
put which will have a velocity for every sample). Both
xsd and flat file (time - velocity - record#) formats
are supported with the default being the latter. This
command line input must be supplied.
-Q qtap
Enter the optional output semblance stack file name.
The traces resulting from the stacking procedure of the
picker can be output as a QC tool. From this one can
see what horizons were picked along the line. There
will be a stacked trace output for every velocity trace
output. This command line input is optional.
-s nord
Enter the length (samples) of the smoother applied to
the semblance profiles for each picked horizon. Default
= no smoothing.
-du devu
Enter the upper % deviation from the guide function.
This defines the upper boundary of the semblance fair-
way. For a function that has increasing velocity with
time the fairway actually gets wider. This and the
lower bound below can be different since in general one
would wish to be somewhat more limiting below the guide
function where multiples are more likely to be encoun-
tered. Conversely, the upper bound can be larger.
Default = 10
-dl devl
Enter the lower % deviation from the guide function.
This defines the lower boundary of the semblance fair-
way. Default = 10
-p pass
Enter the number of alternate peaks to test if the
first peak hits the edge of the fairway. Default = 3
-X Enter the command line argument '-X' to input the guide
function as an xsd pick file, otherwise the function is
in flat file format (see velin documentation).
-L Enter the command line argument '-L' to remove a linear
trend from the semblance velocity profile at each hor-
izon. Sometimes semblances get hotter at lower veloci-
ties even within a rstricted fairway and this can bias
a peak picker toward the lower velocities. Removing a
linear trend can help if this problem exists.
-I Enter the command line argument '-I' to output a velo-
city trace at every original input record number. Most
likely you will have run semblances on say every 4th
CDP record. This option will output a velocity trace
corresponding to every one of the original input
records. It assumes the original RecNum values started
from 1 and incremented by 1, i.e. sequential numbering.
If this is not the case this option won't work.
-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
If one or more of the control semblance records is dead then
the ouput number of records in the line header will be too
large by the number of dead semblance records. This will
also be true of the optional stacked semblance output. It's
probably a good idea to scan the data to determine exactly
how many records there really are then do an in-place utop
to correct the line header.
SEE ALSO
horvel, velspec
AUTHOR
Paul Gutowski with consultation from Kurt Tollestrup, OBU
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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