The regional and local effects of underground injection of wastewater from in situ oil sands pilot plants have been evaluated at sites in the Cold Lake area, Alberta, using projected injection rates up to the year 2015. Geochemical effects were investigated in a suite of cases representative of the injection aquifers and conditions of injection in the Cold Lake Oil Sand Deposit. Although water-rock reactions will take place between the injected fluid, formation waters and minerals in the injection aquifer, only those reactions involving quartz and calcite are significant Based on calculations of the amounts of these minerals precipitated or dissolved, the most important change that should be made to wastewater before injection is softening or the removal of carbon dioxide.

Fracturing thresholds were evaluated at several sites, based on the geomechanical properties of the rocks. The regional effects of deep waste disposal were simulated on a large scale in terms of pressure buildups at 27 sites. Under the assumption that average values of the hydraulic parameters characterize the hydrostratigraphic succession, the numerical simulations revealed no interferences between the different injection sites for the projected duration of operations. The results of regional scale simulations allowed for the individual treatment of each injection site. Local scale simulations were performed for the same sites as were the evaluations of geochemical effects and fracturing thresholds. The results show that vertical fracturing will occur close to the respective injection well at some sites, but overlying strata are expected to prevent fracture propagation to the top of the bedrock. As a general conclusion, the effects of deep injection of wastewaters in the Cold Lake area are felt only in the area adjacent to the injection wells.

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Bachu, S., Perkins, E.H., Hitchon, B., Lytviak, A.T. and Underschultz, J.R. (1989): Evaluation of effects of deep waste injection in the Cold Lake area, Alberta; Alberta Research Council, ARC/AGS Bulletin 60, 64 p.