| OpendTect User Documentation version 4.2 |
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Launch the Well-Seismic Tie window from the main menu.
or
Optionally, the Well-Seismic Tie window can be launched from the tree.
Well to the seismic tie is a major task for interpretation projects. It is used to correlate the well information (logs) to the 3D seismic volume or 2D seismic lines. This enables the comparison (crossplots, ...) of well-based and the 2D/3D seismic data.
Well-to-Seismic tie workflow:
1. Data preparation:
- Import the seismic volume or 2D line.
- Extract a wavelet.
- Import the wells: Each well requires a track, checkshot or time-depth curve and sonic log.
- Import the additional data: 3D/2D Horizons, well markers, additional time-depth curve if a checkshot was loaded.
- Edit the log database: Fill the missing sonic parts, create a density log from the sonic (constant value or Gardner's equation) if not available.
2. Synthetic-to-seismic tie
- The module is launched from the Analysis menu or via the right-click menu of each well.
- The input fields must be selected.
- Based on the available data the density and sonic logs will be combined into impedance and reflectivity, depth-time converted (includes an upscaling) and convolved with the wavelet. The result is a synthetic seismic traces for the well. This trace will be compared with a composite seismic trace extracted in the volume along the (deviated) well path, on the nearest trace. Both synthetic and composite seismic traces are cross-correlated, and the output value is an indication of the alignment and matching quality.
- The alignment will be carried out either by shifting the synthetic trace up or down, or by selecting several locations in both seismic traces, specifying and applying a shift function that varies with the travel time.The applied changes must be validated, before being converted into a new time-depth function that replaces the previous one. No changes are being applied to the well logs.
- At each step of the tie a deterministic wavelet can be estimated using the time-converted reflectivity log and the composite seismic trace. This deterministic wavelet should vary per well, and is known to link the well data to the seismic data more reliably.
The tie well to seismic window is used to select the necessary data for the tie workflow. Please have a look at the introduction to see how to prepare the necessary data.
Well tie can be used to tie the well with the 3D seismic volume and 2D seismic line.
Well to 3D seismic tie window
Well to 2D seismic tie window
The display panel is the main window where the wells are tied to the seismic data. This module is primarly used to update the current (loaded) time-depth curve. Previous, intermediate and final TD curves can be exported to ascii at any moment using the following icon 
.
A secondary output of the synthetic-to-seismic tie is the estimated wavelet, that is estimated at any time and must be saved explicitly.
The view is separated in three frames, from left to right:
- The sonic (red) and density (blue) logs.
- The computed impedance (red) and reflectivity (blue) logs.
- The computed/extracted synthetic and composite seismic traces.
Note: The raw logs are shown before upscaling. The vertical axis of all 3 frames is in travel time.
Key points:
- The time-depth conversion and synthetic seismic traces computation is done using the current time-depth curve and checkshot (if available).
- The checkshot data acts as a strong constraint, i.e. any input and output time-depth curve will be forced to honour the checkshot.
- The time of the depth TVDSD=0 will always remain at TWT=0 even when applying a bulk shift: The difference is absorbed between the point TVDSS=0 and the first sonic log sample. The reference datum elevations definitions are summarized in the well track import chapter.
Display panel for the well-seismic tie.
At the bottom left corner of this display panel, there are several tracking controls. The options are used to pick an event to match the seismic and synthetic traces. After picking the event, press Apply Changes to reflect the changes and update the time to depth model.
Launches the Edit Time/Depth model window. In the pop-up window, press Export button to export the time-depth model as an ASCII file.
Launches the saved option.
The User can either saved the created logs:
Or the User can save the synthetic trace as a seismic volume.
Takes the snapshot of the display panel
Display settings/properties for the panel. The settings are similar to that of the normal 2D-viewer.Change in depth/time model
Zoom-in
Zoom-out
Toggles interact mode ON/OFF
Pick seeds on the seismic or synthetic to update the time to depth model.
Change in depth/time model
- If a checkshot was provided before, there will be two additional options in the well tie window: (1) use checkshot corrections, and (2) display checkshot related curve.
- Choose a tracking mode and select events in the synthetics/seismic displays by first selecting the Pick mode button. Events can not be picked separately. Each event in the synthetics must be linked with an other event in the seismic.
- Once all the events are selected on both synthetics/seismic displays, press Apply changes button. The depth/time model and the whole computational workflow will be recomputed. If needed, repeat the operation.
- The Display additional information button will open the Cross-checking parameters window, and provide useful cross-checking tools, such as correlation coefficient and estimated wavelet in a specific depth range. The estimated wavelet displayed here can also be saved.
- The depth/time table can be saved between each state by pushing the Save button, in the toolbar to the right of the synthetics/seismic displays, and saving with an appropriate name. The View/Edit Model button allows the user to import a depth/time table.
- Once a good correlation has been established, click on Ok/Save and save the depth/time model.
The cross-checking window is launched from the well ties display panel (Section-Well Tie: Display Panel). The window contains the initial and estimated wavelet information. The wavelet can be computed between the two levels (start-end of data in time/depth or markers) that are provided at the top of this window. The window contains further key information: wavelets plot and the correlation coefficient. By changing the compute data between option, the correlation coefficient is auto-updated, this is done by using either Markers (Default) or Time/Depth. After achieving a high and positive correlation coefficient, the estimated wavelet can be saved. Importantly, the negative correlation coefficient shows that the polarity of the estimated wavelet is reversed. To avoid that the reference/initial wavelet's polarity has to be reversed.
Check-crossings window and correlation panel
To save the estimate wavelet, press the icon in the well tie main window .
Moreover, the wavelet properties 
are shown as a graphical display of the wavelet, its amplitude spectrum and phase spectrum.
Save the estimated wavelet
The user can also click on 
to taper the wavelet or to edit the phase rotation:
Rotate Wavelet: Using the slider, the user can edit the phase rotation of her/his wavelet.
Taper Wavelet: This option enables the user to taper a Wavelet. The User will see the real-time changes in the amplitude spectrum.
