NAME
mxcvel - Create/Modify a V(x,z) Velocity Field Dataset from
an mxc model
SYNOPSIS
mxcvel -Nintape -Oouttape -Mmxc.in -Fflag -Uunits \
-mxcvel.crd"\
STARTX NXGRID DXGRID STARTZ NZGRID DZGRID VMAX
startx nx dx startz nz dz vmax
VELO nv X1 Z1 V1 X2 Z2 V2 X3 Z3 V3
1 x1 z1 vel01 x2 z2 vel02 x3 z3 vel03
2 " " "
3 " " "
4 " " " " " " " " "
5 " " "
6 " " "
nv " " "
"
#...|....1....|....2....|....3....|....4....|....5....|....6....|....7
STARTJOB
Create a file that looks like the above synopsis with the
following command:
catpat mxcvel > mxcvel.job
Edit your mxcvel.job with vi to suit your needs and submit
mxcvel.job with the following command:
startjob mxcvel.job
DESCRIPTION
mxcvel creates an interval velocity dataset from a set of
mxc-formatted (x,z) points, or it can modify an existing
velocity dataset. The velocity field may be created with or
without gradients. The input to mxcvel is a set of "mxc-
formatted" (x,z) points, command line arguments, and a set
of parameters and velocity functions read from cards. If an
existing velocity field is input to mxcvel, the resulting
velocity field will be a modified version of the input. New
contours may be added, and the input velocity field will be
used as a backdrop where needed.
Command line arguments
-N intape
Enter the input velocity field dataset name (if any)
after typing -N. If there is no input velocity field,
do not place -N on the command line.
-O outtape
Enter the USP-formatted output velocity field dataset
name after typing -O.
-M mxc.in
Enter the name of the mxc-formatted (x,z) file after
typing -M.
-F flag
Indicate whether the mxc file is in MSTS format after
typing -F. Programs MSTS and MOD2D create mxc files in
MSTS format.
0 = mxc.in did not come from MSTS format (Default).
1 = mxc.in did come from MSTS format.
-U units
Enter the desired units after typing -U.
f or F = feet (Default)
m or M = meters
-h Enter -h for online help. Program will terminate after
printing this.
-? Enter this (or '-?' if you are running in c-shell) to
get online help. The program will terminate after
printing this.
-mxcvel.crd"\
This keyword, -mxcvel.crd"\, must be entered exactly as
shown with no spaces after the backslash. The embedded
menu cards that follow this keyword must be typed
exactly as shown, with the lower case parameter names
being changed to the actual values you want the program
to use. All of the parameter values must be entered in
the correct columns. The double quote following the
embedded menu cards must be present as shown.
Description of Parameters
RTX startx
The desired velocity matrix may start at zero or some
other x-location. The startx parameter indicates the x
location in feet or meters for starting the velocity
matrix. If this value is negative the velocity field
will be extended to the left.
RID nx
The number of traces in the output velocity field.
The output trace spacing value in feet or meters. If modifying a
velocity field, this value should match the input trace
spacing of the input velocity dataset.
RTZ startz
The starting z location in feet or meters.
RID nz
The number of depth samples in the output.
The depth spacing value in feet or meters.
VMAX vmax
The maximum velocity to use for clipping the veloci-
ties. If this value is zero, no clipping will be done.
VELO nv
The number of velocity cards to follow.
V1 X2 Z2 V2 X3 Z3 V3 x1 z1 v1 x2 z2 v2 x3 z3 v3
Velocity gradients are defined using the coordinates
and the velocity for three different points within a
region. Point 1 is defined by (x1,z1,v1), point 2 by
(x2,z2,v2) and point 3 by (x3,z3,v3). For the follow-
ing types of gradients, use the appropriate configura-
tion:
#_______________________________________________________________________
# Gradient
# Type X1 Z1 V1 X2 Z2 V2 X3 Z3 V3 |
#----------------------------------------------------------------------|
#Vertical 0 z1 v1 0 z2 v2 xmax z1 v1 |
#Horizontal x1 0 v1 x2 0 v2 x1 zmax v1 |
#______________________________________________________________________|
FORMAT OF MXC FILE
The MXC format is an early Amoco format for model defini-
tion. Although its usefulness has diminished with time,
there are still occasions where one will encounter this for-
mat. Therefore, we document the "not so easy to decipher"
format here.
#...|....1....|....2....|....3....|....4....|....5....|....6....|....7....|....8
HDR 2 hhh xmin xmax zmin zmax rrrmmmmmmm 1 1 d
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
xxxxx zzzzz
-1.0
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
-1.0
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz xxxxx zzzzz
xxxxx zzzzz xxxxx zzzzz
-1.0
Description of MXC file parameters
DER CARD INDICATOR HDR
The HDR parameter indicates this is a header card.
This is the only HDR card in the deck and is always the
first card. The Fortran format of the header card is
(' HDR',2I5,4F10.3,I5,A7,5X,I1,4X,I1,2X,I1). Numeric
entries (2,1,1) shown on the above card should be
encoded "as-is". The significance of those numbers has
disappeared through the mists of time.
BER OF HORIZONS hhh
Indicate the number of horizons which are defined in
the card file. Horizons must extend all of the way from
the left border to the right border without overturns
(i.e., if we create a curve by connecting the defined
points on the horizon, any vertical slice through the
curve will intersect the curve at one and only one
point).
Indicate the minimum x value to appear in the file.
This is the left-hand border of the model.
Indicate the maximum x value to appear in the file.
This is the right-hand border of the model.
ZMIN zmin
Indicate the minimum z value to appear in the file.
This is the top border of the model. Z values are
entered as positive down.
ZMAX zmax
Indicate the maximum z value to appear in the file.
This is the bottom border of the model. Z values are
entered as positive down.
BER OF REGIONS rrr
Indicate the number of regions or closed contours.
Normally, these points are input from uppermost left-
hand corner, around the region, and back to the upper-
most left-hand corner (i.e., the first point of the
region must be identical to the last point, and digiti-
zation must proceed in clockwise order).
MODEL NAME mmmmmmm
Indicate the 7-character model name.
ON FLAG d
This flag indicates the line direction of the
corresponding seismic data.
-1 = the indices of the GI's, RI's, etc.
increase right to left
1 = the indices for the GI's, RI's,etc.
increase left to right
IZON AND REGION CARDS
There should be a set of cards for each horizon and
each region in the model. A set is defined as a list-
ing of (x,z) points in format (F8.2,7F10.2) followed by
a card containing (-1.0) in the first four columns.
All horizons should be described before defining any
regions and should go from top to bottom. Points in
regions must be defined so that lines connecting points
coincide with the boundaries of other regions (i.e.,
most every point on a region will be digitized at least
twice, once for the top region containing it and once
for the lower region containing it). Failure to care-
fully digitize regions can create ambiguous phantom
regions in the model. Behavior of the different pro-
grams encountering these phantoms is unpredictable.
Some programs have a limit on the total number of hor-
izon and region cards; mxcvel has a limit of 500 con-
tours.
COORDINATES OF POINTS xxxxx zzzzz
List out the (x,z) coordinates of each digitized point.
As four points are entered per card, the last card of a
region or horizon may contain blank entries. Some pro-
grams have a limit to the total number of points per
region or horizon. The limit for mxcvel is 8000
points. Some programs prefer a point with a coordinate
of 0, to be entered as 0.1.
R -1.0
The end of the set of points describing a horizon or
region is indicated by a card containing -1.0 in the
first four columns.
SEE ALSO
mbs, startjob, beginjob, endjob, velin, rmsvel, rmsvlmx,
ivad, swath, vfnd, vtpad, vtrsiz, vtvzex, vttd, xsd2vlmx
BUGS
None known.
AUTHOR
N. D. Whitmore, Jr., Mary Ann Thornton
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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