Oil Sand Fine Tails Absorption Into Overburden Clay Shales-A Dry Landscape Alternative (1991)

Abstract The production of synthetic crude oil results in large volumes of fine tails which will remain as a fluid indefinitely (MacKinnon 1989). The overburden overlying Syncrude's oil sand deposit is a Cretaceous clay shale that is characteristically very dry and exhibits a high plasticity. Syncrude, with the support of AOSTRA, has investigated a technique of combining these two waste products together 10 form a soft clay which is incorporated into stable waste dumps. Laboratory, field and analytical studies have been conducted to determine the geotechnical design parameters required for the construction and behaviour of the dump components, specifically, the containment ribs, the soft clay polder material and the equipment bearing layer. The studies lead to a large scale field test which utilized operations scale equipment. This paper discusses the results from the studies as well as the conclusions reached from the field tests. The work has increased the for fine tails wastes. This could lead to more effective knowledge base with regards to dry landscape alternatives for a safe disposal reclamation option development of oil sand leases. Introduction Syncrude Canada Ltd. operates an oil sand mine in Northern Alberta producing about 10M m3 of synthetic crude oil per year (Figure 1). Annually, 120M t of oil sand are mined. Bitumen is extracted From the oil sand utilizing a hot water flotation extraction process. The solids in the tailings are comprised of a coarse fraction (&gt;22 µm) that readily settles out to form the sand dykes and beaches of the tailings pond, and a finer fraction (&lt;22 µm) which flows as a thin slurry into the pond. Here, the finer fraction settles out relatively quickly resulting in a released or "Free" water zone in the upper part of the surface zone below which the fine tails increases in density with depth (MacKinnon 1989). At current mining levels about 15 - 20M m3 of dense fine tails are produced each year. By the end of the current mining permit life in 2018, approximately 6aOM m3 of dense fine tails will have accumulated. Containment, in the long and short term, is an immediate planning issue and imposes constraints on the lease development plans. In the current mine plan, an integrated reclamation scenario is envisioned involving wet and dry landscapes. In the wet landscape option the fine tails will be disposed into the mined-oU1 pn and capped with a water layer. The water will isolate the fine tails and should allow for the development of a self-sustaining aquatic ecosystem (MacKinnon 1991). In the dry landscape alternatives, the solidified fine tails would be abandoned as a trafficable geotechnically stable deposit on which vegetation will develop. One dry landscape option, which will be described in this paper, is based on the dewatering of fine tails taking advantage of the high water absorptive capacity of the high plasticity overburden clay shales. Background The potential for absorbing fine tails into overburden waste dumps was identified as a component part of a scheme to remove and transport overburden using dredging and pipeline techniques (Lord and Isaac 1989).