NAME
vspvel - extract velocities from processed VSP data
SYNOPSIS
vspvel [ -Nntap ] [ -vvtap ] [ -fvtab ] [ -Xxtab ] [
-sw1swrd1 ] [ -u1unit1 ] [ -sw2swrd2 ] [ -u2unit2 ] [ -sttst
] [ -sosmooth ] [ -V ] [ -? ]
DESCRIPTION
vspvel takes processed VSP data and extracts interval, rms,
and average velocity vs two-way time and depth. This is done
by combining first arrival times with the known sonde depth.
Output is a table and/or velocity traces. Processed in this
case means the VSP first breaks have been properly picked
either (1) by careful picking on xsd plots, or (2) by run-
ning picker (an automatic picker which uses a guide func-
tion). Either way the proper pick values must be written
into the trace headers.
Depth for the sonde must be in the trace header word GrpElv;
source offset from the well must be in the trace header word
SrPtXC.
It is strongly recommended that the user read the basic USP
note VSP Processing in USP by Mile Mueller and Paul Gutowski
before using this tool. If not available locally it is
available upon request from any USP group member at TRC.
vspvel gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
the static trace header words to use, the global start time
shift, the smoothing length, and verbose printout, if
desired.
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. 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'.
-v vtap
Enter the output velocity tape data set name or file
immediately after typing -v. 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 vtab
Enter the name of the file to capture the tabular
velocity information. This file consists of 6 columns:
depth (ft,m), 2-way time (ms), distance from source to
receiver (ft,m), interval velocity (ft,m/s), rms velo-
city, and average velocity. If no file name is given
there will be no tabular output.
-X xtab
Enter the name of the file to capture the optional
xgraph format file. This file when plotted will display
interval, RMS, and average velocity vs depth all on a
single graph. The output will have depth as the X-axis
and velocity as the Y-axis.
-sw1 swrd1
Enter the first static word to use. If picker has been
used to pick first arrivals this is usually the time
given by the guide function. The total travel time used
to the first break for any receiver depth will be (tst
+ unit1 * swrd1 - unit2 * swrd2)
-u1 unit1
Enter the factor with which to scale the swrd1 values
found in the trace headers. If in applying the pick
times a scaler of 10 was used then here the inverse
must be applied, e.g. 0.1
-sw2 swrd2
Enter the second static word to use. If picker has been
used to pick first arrivals this is usually the resi-
dual times around the guide function. The total travel
time used to the first break for any receiver depth
will be (tst + swrd1 - swrd2)
-u2 unit2
Enter the factor with which to scale the swrd2 values
found in the trace headers. If in applying the pick
times a scaler of 10 was used then here the inverse
must be applied, e.g. 0.1
-st tst
Enter the global time shift to apply to the sum of the
appropriate header word scaled times. This is to take
care of any bulk shifts in the recording times. This
will not have any effect on the interval velocity vs
depth calculation.
-so smooth
Enter the length in samples of the smoothing window
applied to the summed trace header times. No matter
how good a job of picking has been done there always
will be deviations from a smooth line. These deviations
can result in bizarre interval velocities especially if
the sonde depth interval is small. An fft-based
smoother is run over these times to try to reduce time
scatter without homogenizing the times so much that all
detailed velocity information is lost. Lengths of 5-10
are typical but testing here is recommended.
-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.
EXAMPLE
After the picker/rest/fkstrip steps have been completed and
you have the upcoming wavefield then the following will
result in the velocity files being generated:
vspvel -Nupcoming -vvelocity_tape -fvelocity_tabl
-Xvelocity_xgraph -sw1SGRDat -sw2StaCor -u2.1 -st0 -so50
where SGRDat contains the picker guide function times,
StaCor contains the residual picks around that guide func-
tion (scaled up by a factor of 10), u2[] rescales the resi-
dual pick times back to ms, st0 means no bulk time shift
needs to be accounted for, the smoothing order is 50 traces.
The velocity tape is written to velocity_tape, the velocity
table is written to velocity_tabl, and the xgraph file of
all 3 velocities plotted against depth is written to
velocity_xgraph
The table can be graphed by entering
xgraph velocity_xgraph
BUGS
unknown
SEE ALSO
picker
AUTHOR
Paul Gutowski & Mike Mueller
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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