Placing Off-Bottom Cement Plugs: Effects of Density Difference
Bibliographic record
Abstract
Abstract The abandonment protocols of oil and gas wells may vary among regions and countries. Most commonly, however, two or more cement plugs are placed along the well for this purpose. The plugs above the lowermost plug are often referred to as off-bottom. The most used technique to place off-bottom plugs is known as the balanced-plug. Following the Western Canadian practices, wellbores are often flushed with water before the plug placement. A successful placement is achieved when the injected cement slurry accumulates at the target position, over the lighter wellbore fluid. To ensure the long-term integrity of the abandoned wells, the contamination of the injected fluid should be minimized. We develop a hydrodynamic model of the early stages of placement in a representative two-dimensional domain. In our previous works, we considered a fixed density difference between the two fluids and investigated the effect of the injector size and eccentricity. In this study, we investigate the effect of the density difference on the displacement flow and the quality of the accumulated injected fluid. When the density difference is sufficiently large, the front of the injected fluid accelerates after the onset of injection. When the density difference is sufficiently small, the front velocity reduces to a quasi-steady value after an initial acceleration. A transition in the front velocity between the two extreme cases occurs in a moderate range. Except where the displacement flow does not develop, the injected fluid accumulates when the flow destabilizes below the injector. The preliminary results reveal intermittent mixing of water with the accumulated cement slurry. The quality of the cement slurry changes non-monotonically with the density difference.
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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 | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".