Figure 1. West Central 3D model overview. Uppermost surface represents the bedrock topography.
Legend on the right highlights the formations and groups of interest.
A three-dimensional stratigraphic model of the subsurface of western Alberta (Figure 1) was created as part of the Alberta Geological Survey’s 3D geological framework of Alberta. The study area encompasses an area of approximately 43 140km2 and includes 50 geological surfaces and 4 unconformities. A grid cell size of 500 m by 500 m was used with a data density of 2 wells per township. Over 2500 wells were examined and 61 247 formation tops picked from a stratigraphic interval encompassing the Watt Mountain to the Paskapoo formation.
Unconventional hydrocarbon production in this area, related to formations such as the Montney and the Duvernay, have made this area of Alberta a focus for the Alberta Geological Survey. Induced seismic events associated with this activity have made the subsurface geology of this region critical. Applications of this model have already been realized regarding these induced seismic events. By using a submodel cropped to the region of seismic activity, the geology of the area could be examined in detail and probable causes inferred. To date, no regional-scale, subsurface, stratigraphic model has been constructed of this area. Thus, this model has the potential to inform both the public and industry.
Reef trends, relating to the Swan Hills reefs and the Leduc reefs, were mapped in detail. Because these structures occur very deep in the subsurface, below and adjacent to many of the target plays (Montney, Duvernay, etc.), they influence the extent and structure of the overlying formations. This is illustrated by Figure 2, which highlights how the deposition of the Duvernay formation was influenced by the location of the Leduc reefs. Further, the location of the Leduc reefs was originally influenced by the paleotopographic highs created by the earlier Swan Hills reefs (which lie below the Leduc reefs). These reefs define depositional features such as the Wild River sub-basin. Because of the stark, vertical nature of the reef mounds, numerous modelling challenges were encountered. An example of this is noted in Figure 2.
Figure 2. Portion of the 3D model highlighting the Leduc reefs and Duvernay formation.
The sub-Cretaceous unconformity is the most regional of a number of unconformities in the study area. Additionally, three other unconformities were incorporated into the model (Figure 3). These represent periods of exposure and erosion of the underlying formations. Figure 3 outlines, in cross-section, the complex relationships between the four unconformities and the underlying strata. Each unconformity is labelled according to its geological time of occurrence.
Figure 3. Schematic illustrating the numerous unconformity surfaces and their relationships to one another.
The regional extent of the unconformities varies with time, with the sub-Cretaceous being the most regionally extensive.
Figure 4. Maps showing the regional extent of erosion related to each unconformity.
Detailed mapping of the sub-Cretaceous unconformity has revealed paleotopographic features such as the Fox Creek Escarpment and the Spirit River Valley.
Figure 5. Modelled surface of the sub-Cretaceous unconformity.
- Refine Elk Point and Cambrian stratigraphy
- Increase the stratigraphic resolution for integration with geohazards investigations
- Integrate groundwater and hydrocarbon resources
- Combine with the structural database to integrate structure within the model