Stratigraphy

This module supports hierarchical naming of units, with supporting tools like lithology selection.

Although a stratigraphic framework can be used independently of any geometry, an easy way to think about it is how it could be used for wells. Every layer in a well can be interpreted as being a specific instantiation of an abstract unit defined in the framework. For example, a sand layer in the upper cretaceous could be labeled cret.upp.sand . Two layers further a similar sand layer can have the same label. Both are then instantiations of this cret.upp.sand 'template unit'.

A classification system invariably has a tree structure. The nodes in the tree are stratigraphic units, the leaves are lithologies. Every unit can have a number of properties (porosity, sand/shale ratio, etc.).

A well interpretation defines a linear sequence of instantiated units, i.e. instantiations of the stratigraphic framework are often simply lists of units. Keep in mind that this is not necessary: any network of connections (not just the array-like ordering) between instantiations may be interesting in certain problems.

To implement these thoughts the separation 'reference data' and 'actual subsurface unit' has been made. A layer is a unit that holds a pointer to a conceptual unit (e.g. there are a couple of sand layers connected to the cret.upp.sand reference data).