Geoshare Data Model, Version 13.0

217-VELOCITY-FUNCTION

Description    Attributes    Comments    References   

Description

A velocity function. This represents the depth-to-velocity mapping for a given vertical line, whose surface location can be a map location, the location of a well, or a location in seismic coordinates.

Description    Attributes    Comments    References   

Attributes

Description    Attributes    Comments    References   

Comments

1. FUNCTION-ID   C=1, R=ULONG   MAND   
         

   Unique number identifying the velocity function.

2. LOCATION   C=1, R=OBJREF      
         

   Reference to a 217-MAP-LOCATION object giving location of the velocity function. Senders are strongly encouraged to provide the location regardless of what other location information is available from the context of the function.

3. SEISMIC-LINE-TYPE   C=1, R=USHORT   COND   
   SEISMIC-SVY-NAME   C=1, R=ASCII   COND   
   SEISMIC-LINE-NAME   C=1, R=ASCII   COND   
   SEISMIC-LINE-NUMBER   C=1, R=FSING1   COND   
   CDP   C=1, R=FSING1   COND   
   SHOT-POINT   C=1, R=FSING1   COND   
         

   Information with which to connect the velocity function to a particular seismic trace if the function is strongly associated with a seismic trace. The SEISMIC-LINE-TYPE and SEISMIC-SVY-NAME attributes are required when the velocity function is associated with seismic data, or with given seismic coordinates. What other seismic-related attributes are required depends on SEISMIC-LINE-TYPE Code values as indicated in the following table:

   Seismic Line Type
   Code	Line Type	Attributes Required
   30	2-D	SEISMIC-LINE-NAME SHOT-POINT
   31	3-D-I (in-line)	SEISMIC-LINE-NUMBER CDP
   32	XLN (cross-line)	SEISMIC-LINE-NUMBER {of the whole cross-line} CDP {within the cross-line}
   33	RANDOM	SEISMIC-LINE-NUMBER CDP

4. UNIQUE-WELL-ID   C=1, R=ASCII      
         

   Unique well identifier associated with this velocity function.

5. ELEV-REF-HEIGHT   C=1, R=FDOUBL      U
         

   Elevation of the function working datum with respect to the ELEV-HISTORICAL-REF (reference datum) in the controlling 217-CARTOGRAPHIC-PROJECTION . For example, if this has a value of 10 feet, then the function datum is 10 feet above the ELEV-HISTORICAL-REF. In lieu of a value, the working datum should be taken from (in order of decreasing preference) 217-VELOCITY-SET or 217-CARTOGRAPHIC-PROJECTION .

6. FUNCTION-CORR-VEL   C=1, R=FDOUBL      U
         

   Correction velocity value for this function.

7. DELTA-INDEX-CORR   C=1, R=FSINGL      U
         

   Delta index correction value in the same units as the INDEX channel (time or depth). This value, when added to the INDEX vector values can be used for correction from the function datum to the set datum; this correction can be performed even if the function's ELEV-REF-HEIGHT is null. Times are always two-way acoustic travel times.

8. INDEX   C=1, R=OBJREF      
         

   Reference to a CHANNEL object describing the index values for this velocity function. The values may be in depth or time. Times are always two-way acoustic travel times. Depths could be measure depth or true vertical depth. When measure depth is used, the associated well identification should be set in UNIQUE-WELL-ID. If possible, the set of indexes used should be monotonic increasing or decreasing, rather than jumping back and forth on the index domain. A useful convention may be that values should start low (shallow) and increase monotonically to their largest (deepest) value. The following attributes in the associated FRAME object should agree with the content of this set of index values: The domain chosen should match the value of the INDEX-TYPE. Minimum and maximum values should appear in INDEX-MIN and INDEX-MAX, and the index increment, if constant, should appear in SPACING.

9. VALUE   C=1, R=OBJREF      
         

   Reference to a CHANNEL object describing the dependent variable values for this velocity function. The values may be in velocity, time or depth.

   Note:

   The four types of pairing that are expected in the INDEX and VALUE channels are (time, velocity), (depth, velocity), (depth, time) or (time, depth). Times are always two-way acoustic travel times.

10. NULL-VALUES   C=1, R=OBJREF      
          

    Reference to a 217-NULL-VALUE object for defining null or absent values in the data in CHANNELs referenced by this object.

Description    Attributes    Comments    References   

References

• 217-VELOCITY-SET

Geoshare Data Model, Version 13.0

Send questions and comments to Jim.Theriot@POSC.org
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