Compositing: Step by Step

Compositing: Step by Step

The COMPOSITE tool allows users to optimally intercorrelate core data from multiple holes so that all stratigraphic features recovered at a given site are aligned with the same features at other sites, producing a new depth scale which is formally termed the Composite Depth Scale, with depth units of mcd (meters composite depth).

The COMPOSITE tool is used in the following manner:

1. Find two features in adjacent holes which are visually correlative, representing the same stratigraphic level.

2. Define one core as being stratigraphically "fixed" whereas the other core will "move" relative to the "fixed" core.

3. Use the center mouse button to place a RED point on the "fixed" core feature (RED=stop). Use the right mouse button to place a GREEN point on the "moving" core feature (GREEN=go). The mbsf of the reference and the moving points are shown in the status box. Note that the mouse pointer does not need to be on the actual feature, just near where the feature occurs in that hole.

4. A tieline is drawn between the two tiepoints and the program determines the cross-correlation between the two cores at the tieline and for a range of depths away from the tieline. The program determines the average sample interval of the datasets, interpolates these data to a constant average sample interval, then computes the correlation between the two cores for a definable data window (default = +/- 2 meters; user-definable) centered at the tieline, and for a series of leads/lags (the "moving" core moves relative to the "fixed" core) above and below this tieline (default = 1 meter;user-definable).

5. If the two features are precisely correlated then the cross-correlation function is centered; the yellow line defining the position of the maximum cross-correlation will be at the zero lead/lag position. More commonly, the tieline is slightly misplaced and the yellow line will be offset from the zero lead/lag position. (when the pointer is in the correlation plotting window the right mouse button can be depressed and dragged to reveal the statistical results).

6. When you release the mouse button, you are asked "Keep this composite?" If you answer "Yes", the core of the moving point, and all cores below it are shifted down.

7. (Deferred): Splicer allows the user to shift cores based on the calculated optimal (highest) correlation - a more efficient way to intercorrelate multiple-hole core data. The user need only click the "ADJUST DEPTH" button to shift the core to its best position relative to the selected correlation feature.

8. The shifted core will then change color (indicating that the core has been correlated and depth-shifted; default = yellow to blue) and shift to its new depth. The (user-definable) default settings will always shift a core (and all those below it) to the depth where the best cross-correlation occurs. The user can chose to shift only a single core, or shift it using the specified tieline or by a definable depth-adjustment.

__