Course 6: Analyzing AVO/AVA Analysis. Use gassman’s equations to predict velocity Objective...
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Transcript of Course 6: Analyzing AVO/AVA Analysis. Use gassman’s equations to predict velocity Objective...
![Page 1: Course 6: Analyzing AVO/AVA Analysis. Use gassman’s equations to predict velocity Objective accurately predict changes in amplitude.](https://reader030.fdocuments.in/reader030/viewer/2022032722/56649f425503460f94c61bdd/html5/thumbnails/1.jpg)
Course 6: Analyzing AVO/AVA Analysis
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Use gassman’s equations to predict velocity Objective accurately predict changes in amplitude
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Open well (your fluid sub well)> save to another name : file > Save As
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Display logs in time : View > Time Model (also make sure view depth mode is set to ft below KB)
Zoom all
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If you don’t have a check shot survey you can use an estimate of the near surface velocity 9KB elevation of working floor of the derrik. Time shift is calculated relative to this datum. To apply time shift>
Edit > Time Alignment
If you don’t have checkshots > may have to estimate velocity from sonic log to get a default TWT time shift
Generally callibrated using check shots. If not, then need replacement velocity. If not estimate from sonic
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TWT = (Start Sonic – KB Eleb)/(2xReplacement Velocity)
Then insert Well curve
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OK
OK
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To make visible click Log Scales from the Edit > Log Scales drop down
Add 3000, 10,000 to the left and right log scales > OK
File > Save
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Select AVO/AVA Synthetics from the Synthetics drop down on the Well Editor Window
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Select your wavelet and click the save defaults button
OK
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Place your AVO
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View > Aspect Ratio Not 1:1
Then View > Select Curves >
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Select > OK
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Turn off Formation Top Labels, CheckShots and plotting parameter buttons;
Click on Data Area > Enter Start and End Times
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Zoom in
AVO Gas
0-4000
4000-8000
8000-12000
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File > Save As
Then close
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AVO Synthetics – Oil
Select your well >
View > Time Model
Synthetics > AVO/AVA Synthetics
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Wavelets tab > define wavelet > OK
Place synthetics
File > Plot > Default Synthetic Layout
View > Not 1:1
View > Select Curves
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File > Plot Setup
Remove checks from Formation Top Table
CheckShot Table and
Plotting Parameters
Click on Data Area >
Start and End Times
OK > OK
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AVO Oil
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Ready for Wet
Open file> select your well> OK
View > Time Mode
Synthetics > AVO/AVA Synthetics
Specify logs for wet case
Insert into present log display
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Modify layout
File > plot > Default layout display
Not 1:1
Rearrange
View > Select Curves
OK
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Further customize
File > Plot Setup
Turn off Fm Tops, CheckShots, Plotting parameters
Click on Data Area button
Specify Start and End times
OK > Plot Setup > OK to Exit
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Lower amplitudes with water only suggests that the presence of hydrocarbons will produce an increase of amplitude with offset
Close and File > Save As
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Water
Gas
Oil
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Use model builder to
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Select well 5 times
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In the Model Builder Select Edit > Default Correlations
Apply > Close
Yes to default correlations will delete any existing correlations
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File Save > AVO Cross Section
OK> OK
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Create Top and Base correlations
Correlation must intersect sonic and density curves in each well
Create horizontal T1 and Base correlations at top and bottom of cross section
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Use correlation selector to select T1
Then click across the top of the log display
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Zoom all> then zoom in across base >
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Select positions across the base of each log
Zoom all
Model > Create AVO/AVA model
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Make sure stretch / squeeze is selected and then > Done
Rename and enter # of traces > select Logs to Use
Near Offsets
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Select your logs
OK
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Use Repeat Traces > Select all wells > and specify repeat traces
Add> OK
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Specify Datum Elevation and Velocity
Specify maximum offset and any other parameters; then Save Default >
Generate Model Again, these should define the Near Offsets
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Maximize > not 1:1
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Change start and End Times and click OK
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Turn off plotting parameters and click OK to close the dialog
Then save traces to SEGY
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Define output file name (DOS or workstation)
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Now Far Offset trace model will be generated in the Model Builder
Model > Create AVO/AVA model in the menu bar
Leave everything the same accept for model name and max and min offsets (at base) >
Generate Model
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Model appears >
File > Plot Setup
Data Area Dialog change start and end times
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Uncheck plotting parameters > OK
Not 1:1
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Resize the trace model windows and arrange next to each other for comparison
File > Save model to SEGY
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File > Save Model to SEGY option not shown in the on-line course drop down > Keep Clicking to get
Output dialog
Select a save file (far offset … Save > OK > File close all
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In this case model parameters are not saved
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Use well editor to compare traces > load SEGY Traces
Get into Geographix
Data
Modeling
Select Near Offset AVO.sgy
End trace 51 but only 41 specified?
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Insert traces
Then load the far offset traces
End trace to 51 again> OK
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Very subtle I couldn’t see it.
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