Sedimentology and Stratigraphic Framework of the Upper Clearwater Formation at Caribou Lake, Alberta

Stuart C. Tye¹, Wendy Warters¹, Shaurat Sayani¹, Emeline Lamond¹, and Michael J. Ranger^2
1 Husky Energy Ltd., Calgary, AB
² Consultant, Calgary, AB

The Caribou Lake Oils Sands deposit is located approximately 70 km north west of Cold Lake, Alberta (Fig. 1). Husky Energy has proposed a Thermal Demonstration Project for the area using a hybrid production technology comprising both cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD). Calculations indicate an Original Bitumen in Place (OBIP) for the 2.5 sections selected for the project of 220 million barrels. The project will aim to recover 1590 m³/day (10 000 bpd) of bitumen.

The primary reservoir unit within the deposit is the Early Cretaceous (Albian) Clearwater Formation. It overlies the dominantly fluvial sand of the basal Cretaceous McMurray Formation and is overlain by the marine shale of the Grand Rapids Formation. To date, 135 wells have been drilled in the Caribou Lake area that penetrate the Clearwater Formation and 99 of these wells have been cored and analyzed.

The Clearwater Formation forms part of a broad, northwest-prograding depositional system comprising both deltaic and incised valley fill deposits. The lower part of the Formation termed the Wabiskaw member directly overlies the McMurray Formation and comprises a coarsening-upward sequence interpreted as dominantly pro-deltaic to distal delta front deposits at the base and top of the succession respectively. Although the unit may be bitumen-saturated, low reservoir quality due to high shale content has deemed it non-prospective for the project.

The overlying succession within the Upper Clearwater Formation comprises a series of coarsening-upward regionally extensive deltaic regressive parasequences. In the Caribou Lake project area the regional sediments have been eroded by a northwest-southeast trending incised valley (termed Valley B). This valley may represent a complex fill comprising several amalgamated valley fills but the sand-dominated monotonous nature of the facies render the identification of sequence boundaries ambiguous. This valley fill constitutes the main bitumen reservoir on the lease and is interpreted as a transgressive tide-dominated estuarine deposit. The Clearwater Formation is capped by a significant transgressive surface and is overlain by marine mudstone at the base of the Grand Rapids Formation.

The two dominant reservoir facies within Valley B are subtidal sand bars and channels and comprise sporadically bioturbated dominantly fine to medium grained, cross-bedded and planar laminated sandstone with subordinate thin (mm-cm scale) to thick (dm scale) laminated mudstone. These facies are confined to a fairway which extends parallel to the axis of the incised valleys through the central part of the lease and defines the focus area for the proposed development. Central estuary basin and/or marginal estuarine deposits form a third facies which is present in the eastern portion of the lease area and are generally non-prospective. This facies consists primarily of bioturbated, heterolithic mudstone and siltstone. The low diversity of trace fossils and the forms present (dominantly simple structures made by trophic generalists) are indicative of brackish water conditions and contrast markedly in character with the bioturbation present within the offshore marine shales of the regionally extensive deltaic regressive parasequences found outside of the valley complex.

Husky has completed the initial phase of delineation work to define the potential of its Caribou Lake oil sands. In December 2006, Husky submitted an application to Regulators which is currently under review by the AEUB and Alberta Environment. Delineation work started in 2005 and to date 64 wells have been drilled; 52 stratigraphic wells, 6 piezometer wells, 2 Grand Rapids Formation water source wells and 4 McMurray Formation water disposal wells. In Q1 2007 a three component 3D seismic program was shot to assist in mapping the Clearwater Formation over the demonstration area. Following successful approval by the Regulators, construction and drilling for the 10,000 bpd demonstration phase of the project could begin as early as 2008 with completion and plant start-up scheduled for mid 2010. The goal of the demonstration project is to determine the most effective recovery process and define optimum operating parameters for the Caribou Lake oil sands asset. With good performance, Husky would plan to expand the project to a 30,000 bpd commercial phase where construction could begin as early as 2011 to accommodate 2013 start-up. The commercial expansion would require an Environmental Impact Assessment (EIA) and application to Regulators.

Figure 1. Location of Caribou Lake Thermal Demonstration Project

AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada