Thermal Release Of Arsenic, Metals And Organic Compounds From Aquifer Sediments During In Situ Bitumen Extraction
Thursday, December 6, 2018: 11:00 a.m.
Exhibit Hall- C4 & C5 (Las Vegas Convention Center)
The Athabasca Oil Sands (AOS) deposits in Alberta, Canada, are estimated to contain approximately 1700 billion barrels of oil of which 170 billion barrels are recoverable with existing technology. Only 20 % of the oil sands are recoverable through surface mining, whereas the remaining 80 % of the oil sands are located at depths (>80m) that require in situ methods. Bitumen is immobile at reservoir temperatures, however when heated to 200°C, it approaches the viscosity of water. To reduce the viscosity of bitumen for recovery, enhanced thermal recovery methods (e.g. steam injection) are used to increase the temperature of the bitumen to decrease its viscosity. The transfer of radiant and advective heat from steam injection well casings to the adjacent aquifer sediments can increase groundwater temperatures, increasing the solubility of some mineral phases. The dissolution of minerals or mobilization of poorly sorbed elements from the sediments may release arsenic and other metal(oid)s to the groundwater. These mobilized elements and heat may be transported down-gradient, away from the injector well, along groundwater flowpaths. This study heated glacial fluvial aquifer sediments from the AOS under controlled laboratory conditions with the objective of gaining a better understanding of the mechanisms for the release of dissolved metal(loid)s and organic compounds to groundwater. Heating of the sediments and water showed a rapid release of As, with As(III) being the dominate mobile species. Other dissolved ions (Ba, Li, Mo, Si and Al) and dissolved organic carbon (including organic acids) were also released, and some of these elements could be useful for tracing groundwater thermal plumes. The information from these thermal tests is capable of identifying the aquifers with the greatest potential for impacting water quality or releasing gases, which would allow these aquifers to be targeted for more intensive monitoring and risk assessment.