The OpendTect Well object is a single track, logs and markers bearing thing with some global data and possibly a Depth vs Time model attached. Therefore, it is not a POSC well in the sense that it describes the data for one well bore only. This may mean duplication when more well tracks share an upper part.
The well track is a 3D line-segment geometry. The traditional description of the Z value in true vertical depth (TVD) breaks down miserably when horizontal well tracks (and worse) come into play. A much better single coordinate to describe the position in a well is the depth-along-hole (or more correctly distance-along-hole). This is why everything in this module is related to the DAH, not TVD. There are facilities to work with TVD, though.
Further it seems to me that anyone familiar with wells, logs and that kind of concepts should find this module's object model fairly intuitive.
1.7.1