Technical Note 1: Application of 2D-Vertical Groundwater Flow Models to the Interpretation of Measured Field Data from the Athabasca Oil Sands.|
K.U. Weyer Ph.D., P.Geol., P.HG.
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada
© 2009 K. U. Weyer
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