Topic:
How to checkshot correct a sonic log and use that calibrated log to create a synthetic.

Description:
The workflow for checkshot correcting a sonic log and using that calibrated
sonic log to generate a synthetic seismogram. 

Other areas covered are preferred DVT's and wavelets.

Solution:
Datum and elevations: 

Datums and elevations, all well data is measured from total datum, working datum
plus permanent datum. This includes markers, logs, and deviation surveys.
Checkshots can be referenced to anything, that is taken care of by the time and
depth reference elevation.
Working datum is measured above permanent datum.

Getting started:

1.) To start, create a preferred DVT for the well. The Synthetics module will
not open any wells for synthetic generation that do not have a preferred DVT.
One way is to generate a DVT from a sonic curve.

To do this follow the steps below:
   a.) DataManager > Wells > Wells 
   b.) Select the well > click MB1 on 'Log Header' to open up 'Well logs' 
       dialog box > select the sonic log > click MB1 on 'create DVT from
       sonic' > this creates a DVT but doesn't attach it to the well.
   c.) To attach the DVT to the well to make it the active or preferred
       DVT of the well > exit Wells > enter Well+T/D > select the well >
       select the newly created time-depth relationship > click MB1 on the
       associate arrow > click MB1 on 'update' > dismiss.
   d.) To look at the DVT created > enter Time/Depth and choose the DVT from
       the list. 
   Note: The first log sample is used for the velocity to fill to the top
         of log. Make sure you don't have an bad value at the top of log
         or the velocity may be to slow or to fast.

Entering Synthetics:

2.) Enter synthetics > Session Manager > Synthetics 
The default layout will be the first well that has a preferred DVT for a well
and a sonic curve. The default layout will contain a > DVT panel > synthetic
panel (in red) > In the synthetic panel you have the following tracks > Log
track, default log = last sonic curve operated on > time/depth track (created
from sonic log in log track) > RC series > wavelet track (default wavelet =
30hz ricker wavelet) > synthetic seismogram track > seismic track (default =
closest inline or 2dline).

Note: The time/depth relationship inside the synthetic panel (all in red) is
generated from the sonic curve in the synthetic panel log track. It doesn't use
the preferred DVT of the well. To get the preferred DVT of the well to be the
same as the time/depth relationship inside the synthetic panel continue to
follow the workflow.

3.) To select another well choose > File > Well > choose from a set/list/or
import.

Calibrating the sonic curve:

4.) Mode > Velocity Survey > Select checkshot, choose the checkshot to be used >
Select sonic, choose sonic to be calibrated > to edit any checkshots or drift
points click MB3 and choose from move/add/delete.

5.) Once you get your checkshot points acceptable > Calibrate, this will display
the calibrated and uncalibrated log in the Sonic panel.

6.) Save Data > the options to save the edited checkshot, calibrated log, drift
curve, and to make the checkshot the preferred DVT or to make the calibrated
log the preferred DVT. 

Choose "Make checkshot data preferred dvt", this attaches the DVT to the well
automatically > Save

7.) Report will generate a Time Depth listing from the checkshot data or sonic
log information and print to the screen or file.

8.) When exiting Velocity Survey, choose the calibrated log in the synthetic log
panel. The preferred DVT now matches the DVT inside the synthetic panel.

Note:
Each panel, Checkshot, Drift Curve, Scale, Sonic, Logs can be altered in
appearance by clicking MB3 and changing any parameters in the popup box.
A nice display is to display the interval velocities of the checkshots in the
Logs panel. To do this click MB3 in the 'Logs' panel and go to content, under
the available curves select 'Interval velocity'.

If you want to plot this screen you must first in the synthetics panel set the
snapshot parameters to 'Main window with children', then open up velocity
survey and use the snapshot icon from the synthetic window to snapshot the
velocity survey window (the child).

Wavelet Generation:

9.) Mode > Wavelet > 1.) Extract > 'Statistical' extracts a wavelet with the
frequency content of the choosen seismic but only outputs zero phase >
'Deterministic' extracts the frequency content and keeps the phase of the input
data so the output wavelet is the phase of the seismic data > 2.) Analytical >
has seven analytical wavelets, phase, polarity and wavelet parameters can all
be changed > 3.) Time variant > allows four gates with the choice of any
generated or analytical wavelets > Select a wavelet using the 'Select' option
or by entering > Mode > Synthetics > and choosing from the available wavelets.

Note: If you use a 'Deterministic' wavelet when you create the wavelet in the
wavelet extraction window under show statistics it will show the optimal time
lag or calculated bulk shift. It does a correlation between the RC series and
seismic data to define this. You can either use this time lag by setting the
preferences to use it > Parameters > Preferences > Deterministic Lag  > or
the preferred way > mode > synthetics. Why? When you save you synthetic traces
you want the preferred DVT to use the bulk shift also, if you set it in > Mode
> Synthetics > when you save the bulk shift will be available to be applied to
the preferred DVT of the well.

Saving synthetic traces:

10.) There are two ways to save synthetic data > 1.) MB3 in the synthetic trace
track > Save > Create a class or choose an existing class to overwrite > under
'Save DVT' update current DVT, this updates the preferred DVT with any bulk
shifts applied > this is key so that well logs, markers, deviation surveys all
have the same bulk shift applied to them as the synthetic traces have so they
all tie > Save 2.) File > Save > Synthetic data > Select the panel > Select the
synthetic track > select or create a class > create a new DVT, enter new name >
click on 'Save synthetic class' to save all the information.

Posting synthetic in Seis%DV:

11.) Define > Well Appearance > Vertical > Synthetic options > select synthetic
class to display, set display options to preferences > dismiss > Save well
appearance.

Note: 'Synthetic location' defaults to 'both' set this to 'Surface' to start.
Surface displays the synthetic as created, 'placed' displays the synthetic
where it has been placed when using > Tools > Synthetic, to slide the synthetic
up and  down, both displays both placed and created (very messy).










Last Modified on: 13-JAN-99