Derek G. Lee¹, Brian A. Rottenfusser², R. John Knight¹
(1) Petro-Canada Oil and Gas, Calgary, AB
(2) Oil Sands Geological Associates, Calgary, AB

Abstract: The geology of bitumen and associated gas in the Athabasca Oilsands, Alberta, Canada

The Athabasca oilsands in northeast Alberta, Canada contain up to 1 trillion barrels of in place bitumen. To exploit the 90% of the bitumen which is too deep for surface mining, Alberta has been the pioneer in development of Steam Assisted Gravity Drainage or SAGD. The process has had remarkable success with initial field testing and a number of pilots and full-scale SAGD bitumen projects are underway or in the approval stage.

The reason for the success of SAGD in the Athabasca oilsands is the reservoir itself. The majority of the Athabaca deposit is in the Lower Cretaceous McMurray Formation where reservoirs are in high porosity, high permeability, quartzose, fluvial-estuarine channel sandstones which show a multi-lateral, multi-storey stacking pattern that can reach 80 metres to 100 metres thick.

Over much of the Athabasca area gas is in direct communication with the bitumen, either as an overlying gas cap or separated by a water zone. The high potential that SAGD holds for exploiting the bitumen has created major conflict between subsurface mineral lease holders. The high vertical permeability found in the McMurray reservoir means that steam will rise to the top of the bitumen. If steam encounters a top gas or a top water zone that zone will act as a thief zone to steam which will have a significant impact on the ability to produce bitumen. Understanding the sedimentological and stratigraphic relationship of the bitumen and gas reservoirs is crucial in determining the co-existence of the resource and the severity of the problem.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana