Examples of Stratigraphic Layers Usage

The footprint of the data model used to load the stratigraphic layer example is shown in the Figure 5 below. The physical database will include; R_GEOLOGIC_LAYER, R_STRAT_RANK, R_LITHOLOGY tables and the view STRATIGRAPHIC_LAYER on the GEOLOGIC_LAYER table. There are two references to the previously described STRATIGRAPHIC_SURFACE view for reference to the top and base surfaces that make the boundaries for the layer.

Formal Stratigraphic nomenclature definitions generally include three elements. First, there is the name which is taken from the type locality. Secondly, is the position of the layer within the stratigraphic hierarchy, i.e. it�s rank. And finally is an optional label of the dominant lithology. If there is a mix of lithologies this tag is omitted. These three elements are shown in the footprint as support for formal stratigraphic naming conventions. In general use, it is common practice to only use the single attribute �Standard_Layer_Name� to identify a layer. Informal stratigraphic classifications may only use the attribute �Name� to identify the layer.

Figure 5 Stratigraphic Layers Usage

Reference Scope Data - R_GEOLOGIC_LAYER

Stratigraphic definitions must first exist in order for standard geologic names to be loaded. Unlike other reference data in the database, geologic feature values are not pre-populated with any content. The reason is that stratigraphic data is only locally relevant and can be extremely voluminous. We expect users to load their own stratigraphic data directly after creating the project and if there is a need to share these definitions across projects or sites, separated processes will be needed. In Table 4 below, all of the standard layer names given in the North Sea example data are shown as they would be loaded into the data dictionary. R_GEOLOGIC_LAYER provides what is essentially a list of standard names that can be combined with other elements in the project area to build a full stratigraphic layer description. Notice there are no entries in reference scope for informal stratigraphic names. If, over time, informal names achieve common usage they may be added to the data dictionary so they can be shared locally.

Table 4 R_GEOLOGIC_LAYER example values

Reference Scope Data - R_STRATIGRAPHIC_RANK

Formal stratigraphic names include a rank value that allows the aggregation of stratigraphic units into a hierarchical system. The standard set for lithostratigraphy is provided below in Table 5 and a full set of all units is populated out-of-the-box during data dictionary creation.

Table 5 R_STRATIGRAPHIC_RANK example values

Reference Scope Data - R_LITHOLOGY

R_LITHOLOGY provides a list of primary lithology names that can be combined with other elements in the project area to build a formal stratigraphic layer name. This optional information is not included in the example North Sea stratigraphic chart.

Project Scope Data - STRATIGRAPHIC_LAYER

Stratigraphic layer names are assembled in the project area as STRATIGRAPHIC_LAYER instances. The natural key for a stratigraphic layer is; it�s formal name, STANDARD_GEOLOGIC_LAYER; it�s rank, STRAT_LAYER_UNIT; it�s informal name, NAME; and the SOURCE of the definition. The primary lithology from reference to R_LITHOLOGY can be given if needed. The physical database implements STRATIGRAPHIC_LAYER as a view on the GEOLOGIC_LAYER table.

Table 6 STRATIGRAPHIC_LAYER example values

Patterns For Defining Stratigraphic Layers

There is a broad degree of flexibility in the combination of attributes that make up a layer definition. This is because there are strong, conflicting, requirements for both formal and informal stratigraphic name assignments to geologic features. For example, a layer can have either an informal NAME like �M Sand� or a formal name composed of the combined attributes, STANDARD_LAYER_NAME name like �Ekofisk� and the STRAT_LAYER_UNIT label �Formation�, or it include both an informal and a formal name, which amounts to a local extension of a standard name. Similarly, different SOURCEs can be invoked to differentiate how these names apply. Ranking may alter the stratigraphic position of the layer. Also, with the application of sequence stratigraphic methods to interpretation problems, there is a strong trend to include the geologic age as a way of identifying and correlating geologic features by establishing an absolute time based grid for comparison. This trend is very helpful in providing some context for events that link features across geologic time and space.

The example data shown in Table 6 above has a variety of layer data for use in different situations. The instance with ID = �100001� is for a formal name �Ekofisk� provided by NPD in the chart on Figure 1. The instance with ID = �100009� is an informal name perhaps used by a single individual. These informal names may change and develop as the study evolves allowing for a late-binding between the interpretation and name of the feature studied. Also, it is common for an interpretation to combine both formal units that are regional in scope with local informal layers that define stratigraphy at a local level for the reservoir architecture of a field, prospect or trend.

Many geologic studies of stratigraphy describe both surfaces and layers to create a �complete� interpretation. An advantage of this approach is its richness and ability to include measurements and properties of the layers along with the names of the surfaces that delimit them. However, the complexity of the data organization requires careful construction of feature associations.

Stratigraphic Layers Loading Sequence

1.    Load the required list of reference layer names to R_GEOLOGIC_LAYER. Remember that any requirements for integration or sharing of this standard list of names must be arranged separately.

2.    Check the available reference data provided in R_STRAT_RANK and make extensions if needed.

3.    Check the available reference data provided in R_LITHOLOGY and make extensions if needed.

4.                  Create (assemble) instances of STRATIGRAPHIC_LAYER with attributes STANDARD_LAYER_NAME (foreign key references to R_GEOLOGIC_LAYER), STRAT_LAYER_UNIT (foreign key references to R_STRATIGRAPHIC_RANK), PRIMARY_LITHOLOGY(foreign key references to R_LITHOLOGY), provide NAME, and SOURCE as needed. Additionally, add values for GEOLOGIC_AGE and GEOLOGIC_AGE_DURATION if there are any expectations to use sequence stratigraphic methods or to apply a consistent time based grid to geologic objects.

5.    Repeat steps 1 through 4 for each project STRATIGRAPHIC_LAYER. Remember that formal names are a combination of STANDARD_LAYER_NAME, STRAT_LAYER_UNIT , and PRIMARY_LITHOLOGY and may not have values for NAME. Informal names may not have formal STANDARD_LAYER_NAME names.