Lower Cretaceous Facies Distribution in the Seal Region, North-Central Alberta: Evolution of a Transgressive Estuarine Depositional System

Lower Cretaceous siliciclastic deposits in the Peace River region of north-central Alberta are estimated to contain 83 billion barrels of oil. In the Seal region these Aptian-Albian aged deposits consist of fluvio-marine units of the Gething Formation and overlying estuarine deposits of the Bluesky Formation. These sediments are capped by open marine shales of the Wilrich Member.

Well logs and core data were used to establish eight distinct facies, grouped into five facies associations. Environments of deposition were determined through this classical facies analysis, supplemented with the construction of a series of reservoir horizon slice maps. These maps, comparable to seismic amplitude horizon slice maps commonly constructed for the exploration and exploitation of hydrocarbon reservoirs, average the lithology of successive 4-meter intervals through the interval of interest. A high-density well dataset, high quality gamma-radiation logs, and numerous drill cores make this methodology feasible. These maps were used to constrain stratigraphic architecture and provide additional insight into the depositional history.

Two major depositional systems were defined in the strata studied: an initial brackish water embayment with an associated tidally-influenced delta, followed by an inner estuary bayhead delta and central embayment complex, in which a local fluvial point source contributed widespread sands to the upper reaches of the estuary system. These deposits are the primary host for exploitable bitumen reserves in the area. This study demonstrates the functionality of facies distribution maps for the purposes of resource delineation and the development of predictive depositional models.