NAME
tvd - module to compute [time, velocity, dip] tweak func-
tions using an input XSD pickfile model of structure and an
input TDFN velocity model. These functions are used by pro-
gram tvdin and tvdnmo to apply the calculated tweak to the
data in the CEP Demult process.
SYNOPSIS
tvd [ -Mdipmodel ] [ -vvelocitymodel ] [ -v0v0 ] [
-msosmoothop ] [ -mssmodelshotstart ] [ -mnsmodelnumshots ]
[ -msimodelshotint ] [ -assanalysisstartshot ] [
-aseanalysisendshot ] [ -asianalysisincshot ] [ -tmaxmaxtime
] [ -gapgap ] [ -gigroupinterval ] [ -sishotinterval ] [
-nchannumchannels ] [ -dirboatdirection ] [ -domend-
pointdomain ] [ -twtweak ] [ -opcoffsetpercent ] [ -V ]
DESCRIPTION
tvd given an input dip and velocity model, computes the
velocity and dip that will nmo shift the model events into a
given quadrant of fk space. The time amount of the shift
(ms) at about the half offset point is referred to as the
(tweak). An event that is tweaked up and away from an
observer standing at the source is termed a (green) tweak.
An event tweaked down and away from the same observer is
termed a (red) tweak. The dip model is supplied as an XSD
pickfile customarily picked from a neartrace display of the
data being processed. Indexing in this file is treated as
sequential. The velocity model is supplied as a TDFN format
function using the same sequential indexing as assumed in
the dip model. This was done to make life easy for the
user. One must simply plot in XSD the near traces of your
data, pick the control dip model for the events that you
wish to tweak, and supply a simple velocity file to go along
with it. This can be readily created from preexisting data
or by running a velspec analysis on the data to be pro-
cessed. Since the process is completely run from a model no
actual USP dataset need be attached. Of course some infor-
mation regarding that dataset is required such as the shot
interval, group interval and gap associated with the
acquisition. Also required is the maximum time of the data
being processed. This will ensure that the functions gen-
erated span the entire dataset for application through tvdin
and tvdnmo.
Command line arguments
-M dipmodel
Enter the name of the XSD pickfile containing your
input dip model. This would be picked from a simple
near trace display of your time data. The model may
contain as many or as few interfaces as you wish. Hor-
izons need not extend across the entire model.
-v vvelocity model
Enter the name of the TDFN format velocity model. This
model should span the entire dataset. If not a static
extrapolation will be done [the outermost value will be
extrapolated to the edges.
-v0 v0 [default = 1500]
Enter the velocity at time zero in ft or m/sec if not
already present on your input velocity model.
-mso smoothop [default = not used]
Enter the smoothing order to use if you wish to smooth
the horizons prior to extraction of dip information.
-mss modelshotstart [default = 1]
Enter the numeric shot for the first location in your
model. This is usually unity as most sequential sets
will start from one.
-mns modelnumshots [required]
Enter the number of shots present in your model. If
you have picked your model from a near trace display of
your endpoint data this will be the number of records
in the dataset to be processed. What we want here is a
model that traverses your entire dataset.
-msi modelshotint [default = 1]
Enter the shot interval used in your model. Unless you
have displayed every other record or some such thing in
XSD this will generally be unity and hence may be
defaulted.
-ass analysisstartshot [default = 1]
Enter the shot location of the first desired analysis
location at which an output [t,v,d] tweak function will
be calculated.
-ase analysisendshot [default = all in model]
Enter the shot location of the last desired analysis
location at which an output [t,v,d] tweak function will
be calculated.
-asi analysisendshot [default = 1]
Enter the shot interval at which tweak functions will
be calculated.
-tmax maxtime [required]
Enter the maximum time [in milliseconds] of your
dataset for which the functions are being generagted.
-gap gap [default = 0]
Enter the distance from the source to near offset in
the units of the dataset.
-gi groupinterval [default = 12.5]
Enter the group interval of the data to be processed in
the units of the data.
-si shotinterval [default = 25.0]
Enter the shot interval of the data to be processed in
the units of the data.
-nchan numchannels [default = 240]
Enter the number of channels in spread of the data to
be processed. This is usually the number of traces per
record of the dataset from which the model was derived.
-dir dir [default = rl]
Enter rl if the shooting direction is from right to
left on the model or lr if the acquisition direction
was left to right on the model. This parameter [along
with -dom below] allows the routine to determine which
side of the [T-x] diagram to be basing the calculations
on.
-dom dom [default = shot]
Enter the common endpoint domain that the associated
dataset is sorted to. Valid entries are shot and
receiver. This parameter [along with -dir above] allows
the routine to determine which side of the [T-x]
diagram to be basing the calculations on.
-tw tweak [default = 25ms]
Enter the desired tweak in milliseconds. This is the
approximate time [at the half offset distance] that
the model events will be moved above [or below] flat.
-opc offsetpercent [default = not used]
Enter percent of the spread to use in calculation.
Note: This parameter is only usefull when experimenting
with tvd in areas of severe structural complexity (
where CEP Demult is of limited use ) and should nor-
mally be defaulted. If you are coming up on a syncli-
nal axis you may want to make this a small percentage
of the spread so that the dip used at each analysis
location is more representative of the near offset sec-
tion of the record. In this routine there is no facil-
ity to handle variations in dip within a single record
along a single event.
-V Include on command line to get verbose printout.
HOW TO
An outline of procedure would look like this:
- Plot in XSD a near trace display of the data to be pro-
cessed.
- Pick a control dip model from this display. This may be
a model of primaries or a model of multiples.
- Generate a TDFN velocity function set over the extent of
the model.
- Run tvd to generate as many tweak functions as required
for your purposes.
- The output of tvd is converted to velocity, dip traces
using the USP routine tvdin. This is very much the same
approach as using velin to associate a velocity dataset with
a USP seismic datset.The difference here is that an addi-
tional dip trace is also created.
- Use the USP routine, tvdnmo, to apply the tweak functions
to the endpoint data.
- Filter the tweaked data with you choice of filters [to
attack either primary or multiple]
- Remove the tweak function through the inverse application
of tvdnmo.
- Apply nmo to the data using tvdnmo with the dip multi-
plier set to zero.
- Examine the result and determine in a time varient sense
the set of tweaks to be used to process your data.
SEE ALSO
xsdtweak sunlay sunform sunhybrd tvdin tvdnmo qdchop bdimage
headerscan fetch usparg
AUTHOR
P.G.A.Garossino, Dec,1997
(original code by Garossino & Bush, Cairo, 1988)
(original USP implimentation by Paul Gutowski, 1989)
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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