Search

The platform carbonates of the Upper Devonian Grosmont Formation hold an estimated 50 billion m3 of bitumen in place and therefore host a significant amount (one-sixth) of the total bitumen resources in northern Alberta. However, unlike the overlying Athabasca oil sands, the bitumen resource has not been tapped as yet. The present study is an overview and integration of recent subsurface studies, largely focused along the eastern subsurface erosional edge of the Winterburn Group in northern Alberta. The basis of the regional geologic framework includes a detailed study of 42 cores with an emphasis on facies description of both reservoir and nonreservoir facies, and the summary of a diagenetic sequence model to demonstrate the major influences on bitumen accumulation. The Grosmont Formation carbonates have been subject to various stages of diagenesis, including dolomitization and karstification with a profound effect on the distribution of porosity and permeability, which resulted in highly heterogeneous reservoirs. In addition, low effective permeabilities because of high bitumen saturation, the high viscosity of the heavily biodegraded bitumen, and the continuity and integrity of shales capping bitumen-bearing reservoir facies are further factors that must be considered in applying future in-situ recovery schemes to the Grosmont carbonate bitumen deposit. [ABSTRACT FROM AUTHOR]

At the Muskeg River Mine, bitumen is hosted in the clastic sediments of the lower Cretaceous McMurray Formation. Within the mine area, the McMurray Formation is divided informally into mappable units representing fluvial, continental floodplain, open estuarine, estuarine channel complex (ECC), and marine environments. Fluvial, open estuarine, and ECCdeposits host more than 90% of the mineable bitumen reserves. Bitumen grade is more consistent within the fluvial and open estuarine units (12-15 mass%), whereas ECC sediments are characterized by significant lateral and vertical grade variability (0-15 mass%). In the ECC deposits, bitumen grade is controlled by significant reservoir heterogeneity. Facies assemblages including point-bar deposits (PB), abandoned channel-fills (AC), and tidal flat deposits (TF), create complex internal geometries, architectures and associated reservoir properties. Traditional facies mapping and correlation has proven to be difficult even in closely spaced wells for the ECC deposits of the McMurray Formation; thus, an alternative technique using concepts of Stratigraphic Dip Analysis (SDA) was developed to assess bitumen grade for the deposits at the Muskeg River Mine. This approach involves three main steps: (l) juxtaposing azimuth maps (rose diagrams) over horizon slice facies maps for selected stratigraphic intervals to identify major channel trends (paleo-current directions); (2) comparison of dips, with corresponding sedimentary structures allows for a better prediction and geometries of point bars and abandoned channel-fills; and (3) comparison of dip trends with dominant lithology of facies assemblages and available bitumen grades provides a base for accurate delineation of architectural elements. A detailed case study is presented and shows that this approach provides a base for accurate delineation of architectural elements and confirms that bitumen grade decreases laterally with inferred maturity of point bar successions. [ABSTRACT FROM AUTHOR]

The Albian to Santonian Colorado Group in the heavy oil area of Cold Lake, east-central Alberta represents a relatively condensed section of shale-dominated sedimentation within the Western Interior Sea. These shales form the cap rock to the underlying Clearwater and Grand Rapids formations that are exploited for bitumen extraction. Two cores covering the entire Colorado Group provide a unique opportunity for establishment of a stratigraphic reference in an area that has received attention only for its heavy oil-bearing Mannville Group. Based on sedimentology, geochemistry, micropaleontology, nannofossils, and wireline log data, the Colorado Group was subdivided into the Joli Fou, Viking, Westgate, Fish Scales, Belle Fourche, Second White Specks, and Niobrara formations. The Niobrara Formation was subdivided further into the Verger Member, informal Cold Lake member, and First White Specks Member. Because of this regions small accommodation space and distance to sources of coarse clastic sediment, disconformities are indicated lithologically by bioclastic layers and missing biozones. Foraminiferal subzones revealed two erosional boundaries associated with the Viking Formation. Faunal and floral evidence coupled with wireline log correlations suggest that the Middle to Upper Turonian Carlile Formation, as described from southeastern Alberta, is missing. That extends the Middle Turonian to Coniacian unconformity, as recognized in central Saskatchewan, westwards into Alberta. [ABSTRACT FROM AUTHOR]

Most of the bitumen in the Athabasca deposit is hosted within fluvial, estuarine, and marginal marine deposits of the Lower Cretaceous Wabiskaw-McMurray succession. The present study is an integration of recent outcrop and subsurface studies, mainly focused in the Fort McMurray area of northeastern Alberta. The basis of the regional geologic framework includes outcrop sections (78), detailed core descriptions (165), and a net of subsurface wire-line log sections (14), all framed within modern concepts of regional correlation and sequence-stratigraphy. The paleogeographic evolution of the Athabasca Wabiskaw-McMurray succession includes five main phases: (1) Lower McMurray fluvial as lowstand deposits; (2) the lower part of the Upper McMurray fluvio-estuarine channel complexes which formed during early transgressive conditions; (3) the upper part of the Upper McMurray A sequences as relict bay-fill and marginal marine deposits formed during early and middle transgressive phases; (4) Wabiskaw D valley-fill developed during a relative sea-level drop at the end of Mc-Murray time (valley-incision phase), which was backfilled during the ensuing transgression; (5) Wabiskaw D regional marine shale, deposited during widespread flooding of the main McMurray-Wabiskaw transgression; and (6) Wabiskaw C deposits formed during continued transgression or early regressive pulses. The regional geological framework has both economic and academic significance, providing better documentation and understanding of the compartmentalization of the oil sands mainly the result of the inherent geological heterogeneity of the Wabiskaw-McMurray succession. Such regional correlation and framework will aid in predicting subsurface and surface reservoir quality and in increased understanding of marginal marine and non-marine sequence stratigraphy. [ABSTRACT FROM AUTHOR]