Examples of Stratigraphy Surfaces Usage

The footprint of the data model used to load the stratigraphic surfaces examples are shown in the Figure 4 below. The physical database will include; R_GEOLOGIC_SURFACE, R_STRAT_SURFACE tables and the view STRATIGRAPHIC_SURFACE on the GEOLOGIC_SURFACE table.

Figure 4 Stratigraphic Surfaces Usage

Reference Scope Data - R_GEOLOGIC_SURFACE

Stratigraphic definitions must first exist in order for standard geologic names to be loaded. Unlike other reference data in the database these 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 need to be arranged. In Table 1 below, all of the standard surfaces names given in the North Sea example data are shown as they would be loaded into the data dictionary. R_GEOLOGIC_SURFACE 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 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 1 R_GEOLOGIC_SURFACE example values

Reference Scope Data, - R_STRAT_SURFACE

Standard definitions may include an explanation of the type of surface described. It is often considered bad practice to mix surface types when establishing a stratigraphic sequence. An example that could be considered incorrect would be using a chronostratigraphic surface to define a lithostratigraphic formation. The full set of stratigraphic surfaces provided out of the box is shown in Table 2 below. If more definitions are needed they should be added.

Table 2 R_STRAT_SURFACE example values

Project Scope Data - STRATIGRAPHIC_SURFACE

Stratigraphic surface definitions are assembled in the project as STRATIGRAPHIC_SURFACE instances. The natural key for a stratigraphic surface is it�s formal name, STANDARD_GEOLOGIC_SURFACE, it�s informal name, NAME, and the SOURCE of the definition. The physical database implements STRATIGRAPHIC_SURFACE as a view on the GEOLOGIC_SURFACE table.

Table 3 STRATIGRAPHIC_SURFACE example values

Patterns For Defining Stratigraphic Surfaces

There is a broad degree of flexibility in the combination of attributes that define a surface definition. This is because there are strong, conflicting, requirements for both formal and informal stratigraphic name assignments to geologic features. For example, a surface can have either an informal NAME like �M Sand Top� or a formal STANDARD_GEOLOGIC_SURFACE name like �Shetland� or include both a NAME and a STANDARD_GEOLOGIC_SURFACE which amounts to a local extension of a standard name. Similarly, different SOURCEs can be invoked to differentiate how these names apply. Also, with the application of sequence stratigraphy to interpretation problems, there is a strong trend to include the geologic age in millions of years 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 in different areas.

The example data shown in Table 3 above has a variety of surface data for use in different situations. The instance with ID = �100001� is a formal name �Sheland� provided by NPD in the chart on Figure 1. The instance with ID = �100009� is an informal name perhaps used by a single individual in his study. 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 picks that are regional in scope with local informal markers that define the reservoir architecture of a field, prospect or trend.

Many geologic studies rely solely on stratigraphic surfaces to create a �wire frame� interpretation. An advantage of this approach is its simplicity. However, surfaces are limited because they do not have any real material properties, such as lithology or water saturation, that can be measured.

Stratigraphic Surfaces Loading Sequence

1.    Load the required list of reference surface names to R_GEOLOGIC_SURFACE. 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_SURFACE and make extensions if needed.

3.                  Create (assemble) instances of STRATIGRAPHIC_SURFACE with attributes STANDARD_GEOLOGIC_SURFACE (foreign key references to R_GEOLOGIC_SURFACE), STRAT_SURFACE_TYPE (foreign key references to R_STRAT_SURFACE), 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.

4.    Repeat steps 1 through 3 for each project STRATIGRAPHIC_SURFACE. Remember that formal names may not have values for NAME and informal names may not have STANDARD_GEOLOGIC_SURFACE names.