--> ABSTRACT: Paleochannel Orientation in Lower Cretaceous McMurray Oil-Sand Deposits from Northern Athabasca, Alberta, by Fothergill, Patrick; Carter, Joan; #90142 (2012)

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Paleochannel Orientation in Lower Cretaceous McMurray Oil-Sand Deposits from Northern Athabasca, Alberta

Fothergill, Patrick *1; Carter, Joan 2
(1) Schlumberger, Calgary, AB, Canada.
(2) Imperial Oil, Calgary, AB, Canada.

The oil-sand deposits of north-east Alberta represent a globally significant reservoir, with approximately 170 billion bbl of initial established bitumen reserves. The majority of this resource is contained within the Lower Cretaceous McMurray Formation, which was deposited in a complex sedimentary succession, with an overall trend of deepening-upward depositional environments from fluvial, to coastal plain and estuarine. Reservoir quality is highly variable and is directly influenced by the environment of deposition. The transition from predominantly fluvial to more estuarine conditions is often associated with an increase in mud content, with attendant deterioration of reservoir quality. In some areas, the lateral accretion of point-bars results in the widespread deposition of inclined heterolithic stratification (IHS), with muddy interbeds negatively impacting net pay. Developing an understanding of the environments of deposition, facies distribution and paleochannel orientation is critical for planning with both in-situ and mining extraction technologies. For in-situ (SAGD) developments the channel characteristics directly influence horizontal well pair planning. For mining developments, understanding the distribution of both reservoir and non-reservoir rock is key to a successful mine plan.

This study uses data from an area in north-east Alberta, and concentrates on the analysis of borehole images to identify the main reservoir facies and to map out paleochannel orientations. The image and open-hole log data have been used to produce a simple reservoir facies classification, which can be calibrated against core and seismic data. Maps have then been produced, which show the changing distribution of facies between the lower and upper McMurray Formation and which identify the stratigraphic intervals with the most widely distributed channel sand. Borehole image interpretations can then be used to look at paleochannel orientation in these stratigraphic intervals, by analysing the azimuth of cross-bedding within channel systems identified in multiple wells. The close spacing of the wells, together with the clear identification of current bedding in the borehole image data, allows high-confidence paleoflow maps to be produced. The results help to delineate a change from fluvially dominated conditions to a more estuarine influenced environment. They also enable channel fairways to be identified, which greatly assists with an effective field development plan.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California