Cretaceous Bedrock Mapping

Cretaceous Bedrock Mapping

Cretaceous Bedrock Mapping in the Area Subject to the Lower Athabasca Regional Plan

What

New and existing lithostratigraphic data have been integrated to generate a regional-scale, high-resolution, 500 × 500 m grid-cell, 3-dimensional model for the Cretaceous succession in northeastern Alberta. The stratigraphic dataset comprises formation- and member-level picks from more than 11 000 wells within the area subject to the Lower Athabasca Regional Plan (LARP).

Why

The Lower Cretaceous Mannville Group hosts most of the bitumen deposits in the Athabasca and Cold Lake Oil Sands areas of northeastern Alberta. Although industry project-scale models have been produced for portions of the Cretaceous succession, an integrated, regional-scale model, constructed using rigorous geostatistical methods, has so far been unavailable. This geologically consistent model will aid efforts to regulate oil and gas activities and to characterize and assess groundwater resources in the area.



Figure 1: Schematic stratigraphic column for the Lower Cretaceous Mannville Group in northeastern Alberta. Red arrows indicate truncation of transgressive/flooding surfaces T21 and T11 at the base of incised valley fills.

Cold Lake Oil Sands
In the Cold Lake Oil Sands area, bitumen deposits lie within a package of stacked incised valley fills in the Clearwater Formation. Valleys were incised during falls in relative sea level and filled during subsequent sea-level rise by sandy estuarine deposits, which form the primary bitumen reservoir. Initial work on this stratigraphically complex interval has focused on mapping areas within which regionally extensive transgressive or flooding surfaces within the Clearwater Formation have been removed by erosion during valley incision. These areas show a clear correlation with bitumen pay thickness (see Figure 2). Future work will focus on picking erosional surfaces at the bases of incised valleys and if possible, modelling the valley fills in 3D.


Figure 2: Map showing bitumen pay thickness of Cold Lake Clearwater deposit from AER ST98-2015.
Incised valleys in lower Clearwater Formation are demarcated by areas within which stratigraphic surfaces T21 and T11 are eroded.