K.U. Weyer Ph.D., P.Geol., P.HG.
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada

© 2009 K. U. Weyer


Introduction

A number of mathematical models for groundwater flow have been calculated in the area of the Athabasca Oil Sands based on the assumption that sizeable 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. The karst in the Devonian limestone has usually been ignored during field investigations and in the setup and calculation of mathematical models. In many places this karst lies directly under the Athabasca Oil Sands.

The presence of karst 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 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.

Hence it is of some importance to provide proof of the widespread downward flow through the oil sands into the karstic limestone and lateral flow towards the regional discharge area Athabasca River. The proof can be supplied through an evaluation of field measurements of water levels in piezometers and the associated equipotential lines. In answer to this question, two 2D-vertical groundwater flow models have been calculated by WDA.

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