Topic:
Sonic curves not calibrated properly in Velocity Survey.

Description:
SYMPTOM: Sonic curves are not being calibrated properly in Velocity
         Survey. In cases that a log starts very close to zero depth.        

Solution:
CAUSE: This is caused when we position the log in time in Velocity Survey.
       Velocity Survey looks at the first checkshots time and depth and 
       calculates a us/ft or meter fill value to fill back to zero time.
 
       If a log has four samples for example to fit 1000 meters and 750 ms 
       worth of fill values back to zero time and depth it may come out to 
       32,000 us/mt's to get the log in time properly.

       There is a clipping parameter that clips everything at 2000 us/mt or ft.
       This doesn't allow the log to be correctly positioned in time when 
       a sonic curve starts at a depth close to zero because of the big 
       value calculated to get the sonic curve positioned in time.
                               
                
RESOLUTION: Put a checkshot level with a zero time at or close to the first
            log value. Then calibrate your sonic curve. Fixed in 10p1.              




Last Modified on: 06-OCT-98