A Deep Look into the Microbiology and Chemistry of Froth Treatment Tailings: A Review

In Alberta’s Athabasca oil sands region (AOSR), over 1.25 billion m3 of tailings waste from the bitumen extraction process are stored in tailings ponds. Fugitive emissions associated with residual hydrocarbons in tailings ponds pose an environmental concern and include greenhouse gases (GHGs), reduced sulphur compounds (RSCs), and volatile organic compounds (VOCs). Froth treatment tailings (FTT) are a specific type of tailings waste stream from the bitumen froth treatment process that contains bioavailable diluent: either naphtha or paraffins. Tailings ponds that receive FTT are associated with the highest levels of biogenic gas production, as diverse microbial communities biodegrade the residual diluent. In this review, current literature regarding the composition, chemical analysis, and microbial degradation of FTT and its constituents is presented in order to provide a more complete understanding of the complex chemistry and biological processes related to fugitive emissions from tailings ponds receiving FTT. Characterizing the composition and biodegradation of FTT is important from an environmental perspective to better predict emissions from tailings ponds and guide tailings pond management decisions.

Field Testing of Selected Salt-Tolerant Screened Balsam Poplar (Populus balsamifera L.) Clones for Use in Reclamation around End-Pit Lakes Associated with Bitumen Extraction in Northern Alberta

For the oil sands mine sites in northern Alberta, the presence of salty process affected water, a byproduct of the hot-water bitumen extraction process, is anticipated to pose a challenge on some reconstructed landforms. The fundamental challenge when re-vegetating these sites is to ensure not only survival, but vigorous growth where plants are subjected to conditions of high electrical conductivity owing to salts in process affected water that may be contained in the substrate. Finding plants suitable for high salt conditions has offered the opportunity for Alberta-Pacific Forest Industries Inc. (Al-Pac) to investigate the potential role of using native balsam poplar (Populus balsamifera L.) as a key reclamation species for the oil sands region. Two years of greenhouse screening (2012 and 2013) of 222 balsam poplar clones from Al-Pac’s balsam poplar tree improvement program, using process affected discharge water from an oil sands processing facility in Ft. McMurray, has suggested an opportunity to select genetically suitable native clones of balsam poplar for use in reclamation of challenging sites affected by process water. In consideration of the results from both greenhouse and field testing, there is an opportunity to select genetically suitable native clones of balsam poplar that are tolerant to challenging growing conditions, making them more suitable for planting on saline sites.

Condensing Solvent Processes: In Search of the Production Function

Summary The heavy-oil- and bitumen-recovery process by injection of a pure condensing solvent in a solvent vapor chamber provides an alternative to steam-based recovery techniques such as steam-assisted gravity drainage (SAGD). Because of the lower operating temperature between 40 and 80°C, the process uses a much lower energy budget than a steam process and thus results in significantly reduced greenhouse-gas emissions. This paper describes the route to a successful production function with the physical processes at play and using analytical tools. Physical relationships are derived for the solvent/bitumen (S/B) ratio, the bitumen drainage from the roof of the solvent vapor chamber, and for bitumen extraction from both sides of the solvent chamber by the draining condensed solvent. The fast diffusion of bitumen into this narrow liquid solvent zone is likely subtly enhanced by transverse dispersion. The speed of bitumen extraction from the roof of the solvent vapor chamber is constrained by the gas/oil capillary pressure. Extraction from the side of the chamber is approximately three times faster by the action of the thin gravity-draining liquid solvent film. Several equations are provided to enable creation of a heat balance for this condensing solvent process. Laboratory and field observations are matched, including the rates, the heat balance, and the S/B ratio. The model can explain constrained production performance by identifying the rate-limiting steps (e.g., when insufficient solvent condenses). The model predicts high solvent holdup during the rise of the solvent chamber. A method to estimate this solvent liquid saturation is provided. The S/B ratio depends on injector-wellbore heat losses, the (high) liquid saturation in the rising solvent chamber, and the process properties (operating temperature), reservoir properties (heat capacity, porosity, and oil saturation), and solvent properties (density and latent heat). In the existing body of literature, no satisfactory analytical model was available; this new approach helps to constrain production performance and to estimate solvent and heat requirements. The methods in this paper can be used in the future for subsurface project design and performance predictions.

Linking hydrocarbon biodegradation to greenhouse gas emissions from oil sands tailings and its impact on tailings management

Microbial research for maintaining soil productivity, health, and environment as well as for ecosystem function has been one of the main research focuses in the Department of Renewable Resources (formerly Department of Soil Science) during the last 100 yr. In recent years, microbial research has been expanded to effectively reclaim disturbed land, remediate contaminated sites, and manage soft sediments such as huge volumes of oil sands tailings. This article highlights the microbial processes in tailings ponds that can affect strategies to manage growing inventory of oil sands tailings and reduce associated environmental footprint. Enormous volumes of fluid fine tailings produced during bitumen extraction from oil sands are retained in tailings ponds. Some tailings streams contain residual labile hydrocarbons originated from the hydrocarbon solvents used in the extraction process. Indigenous microorganisms acclimated to the pond environment metabolize certain fractions of the fugitive labile hydrocarbons into biogenic greenhouse gases (GHG) such as methane (CH4) and carbon dioxide (CO2). Long-term (1–7 yr) biodegradation studies conducted using mature fine tailings (MFT) collected from different tailings ponds reveal that the microorganisms sequentially and preferentially biodegrade hydrocarbons under methanogenic conditions. The stoichiometric mathematical model developed on these biodegradation studies can predict GHG emissions from tailings ponds. Production of biogenic gases also affects the porewater and solid-phase chemistry of MFT and accelerates their de-watering and consolidation during active methanogenesis, which is beneficial for recovery of porewater for reuse in the bitumen extraction process and for effective reclamation of consolidated material.