Thermohydrochemical Model to Identify the Impact of Bleed Flow on Calcite Scaling in a Standing Column Well
Bibliographic record
Abstract
The interest towards standing column well (SCW) is increasing due to their higher thermal efficiency and a lower initial construction cost compared to conventional vertical ground heat exchangers. The SCW pumps and reinjects the groundwater inside the same well. They are usually coupled with an injected well to discharge a portion of the pumped groundwater, an operation called “bleed”, to increase punctually the thermal capacity of the system. Since groundwater is the heat carrier fluid, clogging issues can develop if detrimental conditions are locally present. The most common issue for hard water is calcite scaling. The impact of SCW on calcite precipitation had already been studied with a thermohydrochemical model and field experiments. However, it still lacks a reactive thermohydrochemical model calibrated with field acquired data. Once calibrated, this model could help defining the best strategy to avoid calcite precipitation.A full-scale SCW was operated with a geothermal mobile laboratory for 70 consecutive days. A fractured zone intersects the SCW close to the surface. The operation corresponded to a heat injection with different flow rate sequences. In addition, a groundwater treatment unit installed in the laboratory was used to test different treatment sequences. During this experiment, 20 groundwater samples were collected and analyzed. Those analyses focused on the physico-chemical parameters and the major ions. A reactive thermohydrochermical model was developed in the Comsol Multiphysics environment. This model includes a complex geometry, groundwater flow, heat transfer, and reactive solute transport. The reactive solute transport is composed of two parts; the transport and kinetics model for three primary species and the chemical equilibrium of nine secondary species of calcite reaction. The calibration is achieved by imposing operational parameters as input variables for hydraulic and thermal model as well as the initial concentration.The calibration identified the presence of CO2 degassing. The parameter with more influence on ion calcium concentration is bleed flow. In fact, bleed operation generates a groundwater flow of native groundwater toward the SCW. During this operation, the fracture contributed up to 33 % of the total calcium flux coming to the SCW. This flux is a convective flux. The concentration of total calcium transported by the fracture is closed to the initial concentration. As a consequence, the ion calcium concentration stabilized near the initial state. Thus, the groundwater treatment performance is minimized. The saturated index of the calcite is above zero. On the opposite side, when bleed is not activated, the groundwater is recycled is the SCW. As a results, the treatment unit is responsible of the observed decreases of the ion calcium concentration. The saturated index decreases below zero after five days. Also, when the total calcium concentration decreases in the SCW, a diffusive flux emerged into the fracture.In conclusion, this study highlights the alteration of the solute transport as a function of the bleed operation. The type of flux depends on bleed and the treatment. In addition, the treatment of groundwater is unnecessary when bleed is activated.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".