1. Synthetic Seismogram Objectives
Make Well Section
Quality check and edit logs
Create an Estimated log
Import Check shots
Correct sonic log and establish Time-Depth relation
Make Acoustic Impedance log and Reflection Coefficient Series
Generate Synthetic and Extracted Wavelets
Produce Synthetic Seismogram
Compare seismogram with real well seismic
Manual adjustment and event picking
Display of synthetic trace in 3D window

2. Make well section Select New well section window from the Window menu3
Expand the Wells folder and select the appropriate wells 2 1
Expand the Global well logs folder and select the available logs to use
Well section display
A well section is used for display and QC when generating a synthetic seismogram.
This well section can be used later in the Synthetics process to view and compare the effect of using different parameter settings.
When selecting logs from the Global well logs folder, all displayed wells containing the selected logs will have them shown in the Well section panel.
The other option is to select the logs under each well that will be a more inefficient procedure to follow.
Color fill logs by using the Create/edit curve fill tool 4

3. Process overview 1. Select wells 2. Sonic correction 1
3. Time/Depth lookup
4. AI log and RC series
5. Generate Wavelet
6. Synthetic Seismogram
7. Correlate Seismic
Synthetic Seismogram
Synthetics are a separate process in the Process Diagram tab, found under Stratigraphic Modeling.
Input
Fundamental input in the Synthetics process is a sonic log, a density log and check shots. If density logs are missing, estimated density logs can be derived from sonic logs.
In addition, a mathematical wavelet must be defined based on known parameters from the seismic data. Alternatively can wavelets be extracted from seismic data or imported from a file.
The sonic log is corrected by using check shots, giving a velocity log, which is then multiplied with the density log. The resulting acoustic impedance log gives a reflection series which, when convolved with a wavelet gives the synthetic seismogram. Displayed together with conventional seismic data from around the well position, a well tie to seismic can be made.
Manual adjustments based on known well tops can be performed. 2 4 5 7 6 3

4. Log input and QC 1 Input data to Synthetics; Logs: Sonic [s/ft]GR
Sonic
Density
Caliper CS
Input data to Synthetics;
Logs:
Sonic [s/ft]
Density [gr/cm3]
Check shots (CS):
Check Shot Survey (or)
VSP
Additional logs (optional):
GR [API]
Caliper [Hole diameter]
Any other 1
Bad logs must be edited Estimate logs if missing Splice log intervals Manual editing 2

5. Log editing GR
Sonic
From Global well logs Right click on DT and select Calculator
Make expression Sonic_despiked=DT
Use sonic as template
Sample MD from log and select DT as input
Click Enter 1 2 3 4
This log calculator procedure shown, is used to produce a copy of the original input DT log to avoid overwriting it. 5

6. Log editing - Despike
From Global well logs Right click on Sonic_despiked and select Log editor
Change Action #1 to Despike
Use default parameters
Run and view the result in well section
Undo and adjust parameters if not satisfied
Sonic
Despiked 1 2
Despiking the sonic log is used to remove spike values. Since these error readings will accumulate down through the well when integrating the sonic values, they need to be removed before sonic correction is done. 3 4 5

7. Log estimation – Make density from sonic
Right click on the well where an estimated log should be generated
Click on Use existing, select Global Well Log from the list
Set Action #1 to Density from Sonic
Select Input Log
Apply default parameters 1
Sonic
Est.density 2 3
Log estimation in Petrel can produce a range of different logs based on real data. The quality of any estimated log is only as good as the input permits.
Here the density log is estimated by Gardner’s Approximation. Default parameters are used, but will typically change with the sediments depth of burial. 4 5

8. Process diagram
Double click on the Synthetics process under Stratigraphic modeling
Move the mouse over each of the different icons to see hints on how to use them
Select wells to work with and a well section to display any results in 2 3 1
Opens settings page for the object
Create a new object
Opens the spreadsheet for the object

9. Well selection
Select a single well or the Wells folder to work with from the drop down menu
Working with one well only deactivates the Wells tab selection
Clicking None in the Wells tab, activates the separate well selection list 2 1 3
No creation or changes to the synthetic seismogram takes place before Apply or OK is clicked in the process diagram.

10. Load checkshots
Right click on Wells folder and use Import (on selection)…
Make sure Files of type is correct
Access the files by clicking Open
Select file(s) to import 2 4 1 3

11. Load checkshots Fit input parameters (A) to file (B)
Right click on checkshots to open the spreadsheet
Connect to welltrace
Change depth from MD to TVD. Compare TVD and TWT with input file(s) and other time/depth information
Correct data (if needed)
OK (one file) or OK For All (two or more files if in same format) 5 1 A 6 2
Checkshot parameter selection
To make sure that loaded checkshots data is correct, invest some time in parameter selection and try to understand what each of them do. Clicking on an Attribute or Unit entry in the spreadsheet part of the dialog, brings up a pull down menu to select from. Both depth and time datums can be shanged to match the available input data. The acronyms used are as follows;
MSL - Mean sea level, in the file shown, TVDSS refers to TVD sub surface (i.e. MSL)
KB - Kelly bushing elevated from MSL
SRD - Seismic reference datum
CRD - Checkshots reference datum
The greyed out fields under Depth and Time is enterered during project setup in the Templates pane, se Online Help for further details. 3 B 4

12. Sonic correction
Do the Sonic correction based on original sonic and check shots
Use the generated corrected sonic as input in the process
Check Shot Survey
Sonic Log
T.D.R.
Depth
Time 1 2
Sonic correction
In the process of correcting sonic logs, a delta sonic is added to the original sonic to fit the derived times to the checkshots times. Dependent on the method selected, the fit can be exact (with the risk of introducing artificial events into the resulting siesmogram) or a best fit (introducing a residual drift ) based on a poynomal function.
After sonic correction is performed, the quality of the process can be checked by displaying and verifying the objects derived from the correction. Three toggle boxes are found directly under the sonic correction pull down menu, when clicked each will set up a group panel displaying time, velocity or delta time derived objects.

13. Well time/depth relation
Well TDR is defined by generating global time log(s)
Rearrange the priority list using the blue up/down arrows. Mark (green tick) objects to select from
Open Settings for Global time.
Click on Execute to generate the global time log 2
Click on Shared checkshots, select and drop in a source well from the Well filter of a checkshots item. Execute 3
The Time/Depth Relationship (TDR) for wells can be based on any velocity data source. Typically checkshots or corrected sonic logs are used as input. In Settings for the Wells folder, under the Time tab, a priority list for sources to establish TDRs is found. For any given well, TDR is established from the top of the list using only selected objects (with a green tick mark). If the data object does not exist for the well, it goes to the next object down. To rearrange the priority list, click on the item to move and use the up and down (blue) arrows to reposition it.
Click in the selection box in front of the object(s) to include it as a possible TDR source (green tick).
Manual adjustment gives the user an option to manually adjust the TDR based on Well tops.
Shared checkshots uses checkshots from one well to establis tiem-depth relationships in the selected wells. Activate Shared checkshots, select a well from the Well filter of the available check shot item and drop it into the dialog with the blue arrow. 4 1 2 5

14. Acoustic impedance and Reflection coefficient series
In the Seismogram tab, click on Create synthetic seismogram
Select density and sonic log onput
From the Acoustic impedance pull down menu, select the newly created log
Select Density to use
Click on create new object icon to generate an Acoustic impedance log. Settings opens for selection
Click on the Create new object icon for Reflection Coefficients. Select AI log for input and use the new log as input for RC 4 1 6 2
Creating an acoustic impedance log, normally involves multiplying density and sonic logs. If any of these are unavailable, a velocity log can be substituted for the sonic log or using Gardner’s approximation, estimated logs are made in the process. 3 5

15. Synthetic wavelet Ricker Ormsby Klauder Butterworth
Create new object for Wavelet. Open Settings for it 1
Select Synthetic type of seismogram
Ricker 3
Select which Synthetic wavelet to use
Ormsby
Set parameters dependent on the selected Synthetic 2 3
Phase
Klauder 4
Synthetic wavelets are mathematical describing the shape of the wavelet:
Ricker – defined by peak frequency and period.
Ormsby – wavelet designed from four points forming a trapezoid bandpass filter.
Klauder – simulates the autocorrelation of a linear vibroseis sweep.
Butterworth – defined by amplitude, frequency, high/low cut frequency and high/low order.
Wavelet shape
Amplitude
Butterworth

16. Extracted wavelet Bartlett Cosine Hamming Hanning Papoulis
Select Extracted type of seismogram 4
Bartlett 3b
From Input pane, select seismic data and Well. Drop both ino the dialog box using the drop in arrows 1
Cosine 2
Phase 4
a) Set Neighborhood extent for 3D seismic b) If 2D lines are used, set number of traces 3a
Amplitude
Hamming
Select Taper window type
Extracting wavelets in Petrel is a method of statistically describing the shape of the wavelet.
The extraction option gives statistical wavelets from the seismic data at a borehole based on a portion of a 3D volume or 2D line of seismic traces. If 2D seismic is used for extraction, the number of traces to be included in the extraction must be specified. The user can manually define the extraction position.
The taper window is essentially a function of time that is multiplied by a data segment. Its purpose is to smooth or shape the resulting spectrum.
Alternative type of seismogram is loaded from file
Wavelet shape
Hanning 5
Import the file in the Input pane and open it in the dialog box 6
Papoulis
Set Time unit 7

17. * = Synthetic seismogram
Click on the Synthetic seismogram pull down menu to view its content 1
Reflection coefficients and wavelet is input when Apply or OK is clicked
Signal:
S=R*Wavelet
The reflection coefficient series is convolved with the chosen or derived wavelet, giving the synthetic trace that typically is repeated a number of times to ease the display of the result.
Observe that the resulting synthetic seismogram is not created until Apply or OK in the process dialog is clicked. It then takes the defined inputs selected by the user to create the synthetics. * = 2

18. Well seismic extraction
In the Well seismic tab, check the Create well seismic box
From the input pane, click on the seismic data object and drop it in using the drop in arrow
a) Select which extraction method to use, Radial or Orbital (3D) b) Set number of traces to use along seismic line (2D)
Set appropiate parameters for method chosen. 1 2 3a 4
Extracted Well Seismic in Petrel follows the well path of the different wells. For a deviated well, this means that extracted traces for the deviated part is different from the traces higher up in the well.
When extracting from a seismic 2D line, the closest portion of the line will be selected. Manual selection can be done based on line and trace numbers. 3b

19. Synthetic seismogram settings
After generation of the synthetic seismogram, open Settings from the Shynthetics process dialog box
Open Synthetic seismogram tab and set Number of traces to 3. Set Peak frequency Action to Sequence and type in 20 – 25 – 30. Apply and view the result in the well section
Open the 2D Style tab and select Show wiggles. Fill in the preferred parameters 2 1 3

20. Synthetic seismogram spreadsheet
From the Input pane, right click on the Synthetics folder and select spreadsheet
Filter on a single well and set the Domain to work in (e.g. TWT)
Specify Step and Use limit Min. and Max. to filter the spreadsheet 4 1
Color fill the spreadsheet for visual aid to identify features not easily seen 3 2
Selecting the domain to work in, defines the column for which the Step and Use limit entries will apply to. By setting domain to TWT, Step to 2 and Use limit Min. 1000,and Max. 2000, will filter in the TWT column and only show every second row/sample between 1000 and 2000 ms in two way time.
Every change to the filter settings involves a potential display of several thousand rows, so in most cases will an Petrel warning box pop up that need user verification. An option to color fill the content of the spreadsheet is added to help the user identify features that otherwise would be difficult to identify

21. Manual adjustment
Under the Sonic and time tab, with Overide global time log(s) active, check the Manual adjustment box
Updated TWT Picked values can be entered. Click Apply in the spreadsheet to store the manually entered values
Applying the manual adjustment in the Synthetics process will update the TWT auto values to fit the TWT picked values
Open the Well tops spreadsheet
Manual adjustment of the synthetic to the real seismic is based on well tops. If no well tops are available to the project, users can create a set of artificial well tops at levels where easily identified events can be observed. 3 1 2 4

22. Manual adjustment Undo the Manual adjustment
Apply the Manual adjustment and observe the effect in the Well section
In the Well section find a well top which needs adjustment
To edit well tops in time, click and move the well top line to a desired position. The TWT picked value in the Well top spreadsheet will update accordingly
Activate the Edit well top time from the icon bar to the right 7
Create/edit well tops
Show well top time
Edit well top time
When Manual Adjustment is performed (used in the synthet6ics process), the calculated TWT auto is recalculated using the updated TWT Picked values. This is a reversible process since deselecting Manual Adjustment and rerun the process restores the TWT Auto to the original that is based on Time settings for the well.
Alternatively to running the entire synthetics process is to open settings for Wells, go to the time tab and control manual adjustment from there. 6 5 8

23. 3D display
Since a time/depth relationship is established in some wells, Synthetics and Extracted seismic can be displayed in both time and depth
Change time/depth settings to TWT. Alternate between TWT and TVD
Open up an existing 3D window and display seismic lines together with wells, well tops, logs, synthetics and extracted seismic 2 3 1 2

24. EXERCISE Synthetic Seismogram