Depth tie view
The Depth tie view matches and calibrates depth-referenced well data, for example a core or logging run against a reference log. All calibration is done in the depth domain: one track of a well holds the curve that stays fixed, and the curves of another track are shifted and stretched until they match it.
The view is built on the Well correlation view, so it displays the wells of the current well section side by side, and tracks, curves, markers, depth axes, templates, units, zooming and the global, axis and track settings all work in the same way. Only the calibration tools described below are specific to Depth tie.
Creating the view
Go to the Views bar in the Ribbon bar and click Depth tie, the button between Well correlation and Graphs. Wells, tracks and curves are added exactly as in Well correlation.
Reference and Adjustable Tracks
Calibration works between two tracks of the same well. Right-click inside a track and choose:
- Set as Reference Track - the track keeps its original depths and defines the target MD positions. A well has one Reference Track: marking another track as the reference turns the previous one into an Adjustable Track.
- Set as Adjustable Track - the track is the one that is calibrated. A well can have several Adjustable Tracks, and each keeps its own depth shift and its own anchors, so different runs may end up with different calibrated depths.
The header of a track that has a role reads Reference or Adjustable, followed by the curve that is used for matching and, when the curves come from a log run, that run in square brackets.
The same context menu lists the curves of the track as Reference Curve on the Reference Track and as Matching Curve on an Adjustable Track, each followed by the curve name. Click an entry to make that curve the one that is matched; a tick marks the current choice. All curves of an Adjustable Track share one depth axis and receive the same calibration.
A track that stops being an Adjustable Track loses its shift and its anchors and returns to its original depths.
Calibration tools
The header of the view carries the calibration tools. They are shown only in the Depth tie view, and hovering over a button shows its name.
- Shift depth - moves a whole Adjustable Track up or down. Select the tool, then press the left mouse button inside the track and drag vertically. The drag counts as one step for Undo.
- Edit anchors - ties depths of an Adjustable Track to the depths they should have, which stretches and squeezes the track. See below.
- Remove all anchors - deletes the anchors of the selected Adjustable Track. Its depth shift stays.
- Auto shift - calculates the depth shift of the selected Adjustable Track automatically. See below.
- Undo last edit and Redo last edit - step back and forth through the shift and anchor edits made in the view.
- Save calibrated curves - writes the calibrated data to new log runs. See below.
Right-clicking an Adjustable Track adds Reset Depth Shift, which sets the depth shift of that track back to zero and leaves its anchors in place, Remove Anchor, which deletes the anchor under the cursor while Edit anchors is active, and Remove All Anchors.
Anchors, stretch and squeeze
Select Edit anchors and work inside an Adjustable Track. Pressing the left mouse button on empty track space places a new anchor and grabs it straight away; pressing an existing anchor grabs that one. Drag vertically to the depth the anchor should point at and release. Anchors are drawn as horizontal lines across the track, and each drag counts as one step for Undo.
Between two anchors the depths are interpolated linearly, which stretches or squeezes the curves. Above the first anchor and below the last one the offset of the nearest anchor is held, so a single anchor acts as a constant shift and the unanchored part of the track keeps its shape instead of being extrapolated.
The depth shift of the track is applied on top of the anchors, so removing all anchors leaves the shift behind.
Auto shift
Auto shift finds the best constant depth shift for one Adjustable Track by correlating its Matching Curve with the Reference Curve of the same well. Click inside the track to select it, then click Auto shift. The curves are correlated as they are displayed, so the result refines the shift that is already applied instead of discarding it. If the curves have not both been chosen in the track menus, g-Space can identify matching LAS curves by their original mnemonic, so GR and GR 2 can match when both came from GR curves. If no curve has been chosen in either track, g-Space uses the only common curve automatically or asks which one to correlate when several are available. The resulting shift applies to every curve in the Adjustable Track.
By default the whole depth interval shared by the two curves is searched. To narrow it, open the Module properties panel, select the Parameters tab and use the Depth tie cross-correlation params group: Start and End set the depth window and are only applied when End is greater than Start, so the default 0 in both searches the whole overlap, and Max shift +/- limits how far the track may be moved, 50 by default.
A message explains why nothing happened when the well has no Reference Track, when the two tracks have no curve in common, or when the curves do not overlap inside the search window.
Saving the calibrated curves
Save calibrated curves saves every Adjustable Track of every well in the view. Each track is saved on its own, so tracks with different shifts or anchors keep different calibrated depths and nothing is resampled onto a common depth axis.
- A track whose curves come from a log run is saved as a copy of that run with _Calibrated added to its name, for example Core_Run_1 is saved as Core_Run_1_Calibrated. Every curve of the run is copied and only the depth column changes.
- A track that holds the TWT and Vint curves the view builds from the checkshots of the well has no source run, so each of those curves is saved as its own run, TWT_Calibrated and Vint_Calibrated.
The source run and its original depths are never changed. Saving the same track again refreshes its calibrated run instead of adding a second copy. When the view holds nothing that can be saved, a message explains that a track has to be marked as Adjustable and hold either the curves of a log run or the TWT and Vint curves of the checkshots of the well.
See Also