Open File Report 1996-02

Author(s) Date 1988-08-30

This report represents the results of the second year of a two-year jointly funded contract between the Alberta Research Council and Alberta Environment. In the report of the results of the first year (Basin Analysis Group, 1987) the regional geology and natural fluid regime were described for an area defined as Tp 50-70, R 15 W3 Mer to R 17 W4 Mer (60 000 km2), together with numerical simulation of the regional effects of deep waste injection at 27 sites using rates projected to the year 2015.

Not included in the above regional study was the geothermal regime in the study area, and this topic is, therefore, covered first in the present report. It completes the analysis of all natural regional aspects of the study area and provides the basis for evaluation of thermal effects of deep waste disposal.

The major part of this report is concerned with what may be termed local effects of injection. Specifically, they relate to potential water-rock interactions as these affect permeability reduction due to mineral precipitation, the onset of induced fractures during sustained injection of liquid wastes, and the pressure buildup adjacent to the injection well. The geochemical effects of deep waste disposal in the Cold Lake area are presented first, in order to evaluate possible changes in the porosity of the host aquifer as a result of mineral precipitation/dissolution. Significant changes in porosity affect the hydraulic characteristics (permeability, specific storage), therefore influencing the pressure buildups resulting form injection. Given that deep waste disposal is generally a safe operation except for possible vertical migration through conduits such as fractures in the confining formations, it is important to know at what stage in the injection process fracturing will be initiated. Thus, an evaluation of fracturing thresholds for rocks at sites in the Cold Lake area is presented before the numerical simulations of hydraulic head (pressure) buildups. A brief evaluation of transport processes related to deep waste disposal is presented at the end.

The local effects were evaluated at a limited number of sites which were chosen based on representativeness of the injection aquifer with respect to stratigraphy (Basal Cambrian, Cooking Lake, McMurray, Clearwater and Grand Rapids aquifers), areal distribution of wells injecting into these aquifers, data availability and, when appropriate, closeness to injection sites. Based on all these studies it is concluded that the injection of waste waters in the Cold Lake area has only limited local effects close to the injection wells.

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Bachu, S. (1988): Evaluation of deep waste disposal Cold Lake area, Alberta and Saskatchewan: local effects; Alberta Research Council, ARC/AGS Open File Report 1996-02, 391 p.