Automatic Log Correlation Beta Program June 8, 2007

1. Automatic Log Correlation Beta ProgramJune 8, 2007

2. Overview This is an early proto-type for an automatic log correlation algorithm in Elog. The idea is that there is an Auto Stretch button on the conventional Log Correlation Window. Clicking Apply on this button causes the synthetic and seismic to be automatically correlated as shown on the next slide.

3. Overview If this correlation looks acceptable, the user then clicks on Stretch to perform the actual log correlation, as before.

4. Overview There is a Parameters Menu, which controls the algorithm. The user can modify these parameters and click Apply to fine-tune the result. After correlating a particular well, these parameters are saved for application to the next well.

5. Installation The beta program and data are contained in a folder called “Elog beta”. There is a test data set in a folder called “Test Data”. This test data will be most easily accessed if the “Elog beta” folder is copied directly to the C:\ disk location. To start the program, double click on the file “elog.exe”.

6. Running Elog beta The Elog beta program is intended to operate on an existing project, which has been set up using the standard release versions of Elog, Strata, or AVO. To use the Automatic Log Correlation, open the existing project, as shown above. To run the test data, go to the Test Data directory and select the erskine_project, as shown:

7. Running Elog beta Now, click on Correlate to produce the usual Log Correlation window. The only difference is the Auto Stretch button.

8. Running Elog beta The recommended way to run this option is to click on Auto Stretch / Parameters. This allows you to modify parameters and click Apply. Each time you do this, the events will be re-correlated using the specified parameters.

9. Running Elog beta Using the defaults, the correlation looks like this: Note that the log has not been stretched. To do that, you still have to click the Stretch button.

10. Running Elog beta The most critical parameter is the ability to tie 1 or 2 tops to corresponding seismic horizons. This information “guides” the correlation window and is especially useful if the original log is far from the desired final time. This is the setting for the test data: Note that it doesn’t actually make any difference to this particular data set.

11. Running Elog beta A second useful parameter is the Spike Threshold. This allows you to filter out small events and reduce the number of correlations. A Spike Threshold of “1” means keep only those peaks/troughs which are at least (1 times the average amplitude). So a larger number here reduces the number of events. Examples on the test data are shown on the next slide.

12. Running Elog beta

13. Running Elog beta The Window Length specifies the size of the window, which is used to do the correlation. The program finds all the peaks and troughs on the synthetic. Then it removes some of the peaks/troughs using the Spike Threshold. Then for each remaining peak/trough, it calculates the cross correlation with the seismic trace, using a window of this specified length, centered around the peak/trough A longer window gives more stability, but less detail. A longer window also tends to give fewer events. Theoretically, this Window Length should be about the length of the wavelet.

14. Running Elog beta The Maximum Shift is the largest allowed difference between the pick time on the synthetic and the pick time on the seismic. Note that if tops are tied to horizons, this is the maximum shift after performing the shift implied by those ties. Reducing this number can help stop large mis-ties.

15. Running Elog beta The Smoothing parameter controls the smoothing which is applied to the raw correlations which are done with each of the peak/trough combinations. It can help filter out erroneous picks. The default, Median, is usually best.

16. Running Elog beta After clicking Apply on the Parameters menu, the usual Check Shot windows appear. Note that no stretching is actually done until you click Ok on the left menu. Also, note that another application of Auto Stretching can often be helpful, after the first.

17. Running Elog beta This is the result of applying the default parameters. Now, if there is another well to correlate, click on Open Well to select the next well. Note that all the parameters chosen for Auto Stretch will be used as defaults for the next well. When all the wells are done, save the project and exit Elog_beta. Start up the release version of Strata or AVO and continue the project.