Using Heated Column Experiments to Investigate the Effects of In-Situ Thermal Recovery Operations on Groundwater Geochemistry in Cold Lake, Alberta
Bibliographic record
Abstract
Groundwater monitoring studies of the Cold Lake-Beaver River (CLBR) basin in Alberta, Canada have linked increases in arsenic concentration to subsurface heat release caused by insitu thermal recovery operations.In-situ thermal recovery is an extraction technique that is used throughout the CLBR and Athabasca Basins to mine viscous unconventional oil at depths below 80 m by injecting steam through thermal wells at 200°C to 300°C into a target reservoir.As the steam is pumped towards the oil deposit, heat is dissipated from the thermal well into the surrounding aquifer layers over the course of one to two-month periods during the steam saturation process.Aquifer sediments that are exposed to these localized elevated temperature conditions undergo increased rates of water-rock interactions that favour mineral dissolution and desorption of surface complexes.Sulfide and iron oxyhydroxide minerals have been identified in the aquifer sediments as primary carriers of arsenic within the CLBR basin which have the potential to liberate contaminants in potable groundwater sources at near-neutral pH levels.Preliminary laboratory experiments have shown an increased rate of reaction at temperatures >80°C with respect to mineral dissolution and the release of constituents, including arsenic and heavy metals, with aquifer sediments from Cold Lake, Alberta.However, previous studies have not incorporated reactive transport processes into their research.To investigate the hydrogeochemical mechanisms of aquifer heating and solute transport in detail, a series of experiments were performed using a novel heated column design.The heated column apparatus is able to simulate the geochemical reactions and physical flow of saturated aquifer materials in contact with a thermal recovery well, while allowing temperature and water geochemistry to be monitored regularly over time at discrete locations.iii In this study, three separate heated column experiments were carried out using different mineralogical compositions of saturated aquifer materials, while maintaining a temperature gradient of 50°C to 90°C, and a constant flow rate of one pore volume per week.Aquifer materials that were used in the three experiments included: (a) 30/40 mesh quartz sand; (b) 30/40 mesh quartz sand with 0.6% w/w pyrite; and (c) sand and gravel sediments collected from the Empress formation aquifer within the CLBR region.For the experiments that had sediments containing sulfide minerals, the column apparatus was kept in an anaerobic chamber and input water was purged using nitrogen gas in order to better simulate anoxic subsurface conditions.Results from the heated column experiments showed that metal and non-metal constituents were liberated from each of the test materials when subjected to temperatures up to 90°C.Higher concentrations of these constituents were generally found at locations downgradient of the heating area, while comparatively lower concentrations were observed within and upgradient of the heating area.Furthermore, heated column experiments conducted using sulfidic materials in aerobic conditions showed higher concentrations of oxidized species (SO 4 ) and dissolved metals and non-metals, whereas the anaerobic experiments generated higher concentrations of reduced species (HS -, Fe 2+ ) and generally lower concentrations of dissolved metals and non-metals.Mechanisms for the release of constituents under aerobic conditions are consistent with the oxidative dissolution of sulfide minerals, and rapid oxidation of Fe and S species.These processes were found to influence dissolved oxygen, pH, silicate and carbonate buffering, and precipitation of Fe oxyhydroxide minerals.Processes occurring under anaerobic conditions were shown to rely on slower rates of sulfide mineral dissolution and desorption of sulfate and trace metals.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".