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Karstic Devonian Limestone as a Transmitter of Groundwater Flow from Overlying Oil Sands

K.U. Weyer, J. Molson and J. Ellis
Text version of a poster presented at the International Association of Hydrogeologists' 39th IAH Congress, Niagara Falls, ON, Canada, 16-21 September, 2012

2012, WDA Consultants Inc.



Introduction

A number of mathematical models for groundwater flow have previously been developed in the area of the Athabasca Oil Sands based on the assumption that groundwater flow is essentially limited to the Quaternary and Cretaceous layers. The Basal Sands of the oil sands are usually assumed to be the regional aquifer transmitting groundwater laterally. The Basal Sands are not continuous when considered at the scale of leases. Furthermore, the karst in the Devonian limestone has usually been ignored during field investigations and in conceptual and numerical groundwater simulation models. In many places this karst lies directly under the Athabasca Oil Sands. The presence of a continuous karst layer immediately below the Cretaceous layers would provide effective pathways for groundwater flow and pressure changes between injection and depressurization wells and, possibly, flow towards the Athabasca River. In addition, the presence of permeable karst also affects the Steam-Assisted Gravity Drainage (SAGD) operation as pressure losses will occur into the Devonian karst. Therefore higher pressures likely need to be applied and the danger of surface escapes of steam is thus increased. Operating costs will increase as well.

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