Study of chloride migration in Cold Lake, Alberta, Canada

In the Cold Lake area, the Colorado Shale forms the uppermost part of a thick sedimentary bedrock, containing considerable amounts of chloride. Chloride transfer from the shale to overlying fresh-water Quaternary aquifers was studied, using numerical models based on chemico-osmotic and transport equations, and laboratory experiments. The Colorado Shale diffusion coefficient was approximated between {dollar}{bsol}rm1.7{bsol}times10{bsol}sp{lcub}-11{rcub}m{bsol}sp2{dollar}/s and {dollar}{bsol}rm1.27{bsol}times10{bsol}sp{lcub}-10{rcub}m{bsol}sp2{dollar}/s, from diffusion tests conducted on five core samples. Excess pore pressure and chloride concentration variations were studied as well. The chloride migration was simulated with MT3D transport model, for an 8,500m two-dimensional section calibrated with two wells, located south of Imperial Oil Cold Lake Operations. Model parameters included calculated diffusion coefficients and collected field data. The simulation showed that chloride concentration increases in Quaternary aquifers (i) from recharging to discharging areas, (ii) towards bedrock contact, (iii) with hydraulic velocity decrease, (iv) for higher chloride bedrock content and, (v) for higher diffusion coefficients.