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Putnam, Peter E.1, Shawna Christensen1
(1) Petrel Robertson Consulting Ltd, Calgary, AB

ABSTRACT: Distribution of Optimal Steam-Assisted Gravity Drainage Reservoirs within the McMurray Formation (Lower Cretaceous) of Northeastern Alberta

Most of the bitumen resource in the tar sands of northeastern Alberta is currently too deep to mine and is too shallow to be developed using high pressure thermal recovery techniques. As a consequence, relatively low pressure steam-assisted gravity drainage (SAGD) techniques are deemed to be the most effective extraction technology currently available. However, because SAGD runs at pressures below those required for fracturing, thin mudstone beds may significantly impede steam chamber growth and bitumen recovery. In order to avoid the retardation of steam chamber growth during the initial stages of a SAGD project when there is some urgency to recover sunk capital as quickly as possible, it is necessary to initiate SAGD recovery schemes within homogeneous reservoirs with high bitumen saturations. 
The Lower Cretaceous McMurray Formation is the main SAGD reservoir currently undergoing development. However, McMurray bitumen-bearing beds are typically extremely heterogeneous. Consequently, there is a need to determine, in three dimensions, where the thickest optimal reservoirs are located in order to most appropriately locate the positions of injection and production wells. The creation of filter and slice maps, based on the information from 6500 wells, was undertaken in order to determine where the most homogeneous reservoirs (i.e. filter maps) are located in three dimensions (i.e. slice maps). The main findings of the mapping exercise are: 
1. Homogeneous McMurray sandstones with high bitumen saturations that exceed 10 metres in thickness form only a small portion of the resource base. 2. In the eastern portion of the Athabasca deposit, stacked channelized successions predominate. Although the bitumen columns here are the thickest observed, these deposits are extremely heterogeneous with optimal reservoirs displaying a complex distribution. 3. Assuming that truly homogeneous reservoirs will be the sites of commercial development, productivity predictions and reserve estimates publicized by corporations and government agencies may prove to be exaggerated without new technology and/or sustained high oil prices.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.