Bibliographic record
Abstract
Primary cementing of casing strings is a necessary well construction operation where the annulus behind the string is displaced to a cement slurry. Cementing by reverse-circulation involves injecting cementing fluids directly to the annulus from surface, which can reduce the circulation pressure exerted onto the open-hole section during placement. We study density-unstable reverse-circulation displacement flows involving non-Newtonian fluids in near-vertical, eccentric annuli and use a semi-analytical displacement model to assess whether the interface between displaced and displacing fluids will elongate (unsteady displacement), or remain compact as cementing fluids are pumped down the well (steady displacement). We use the displacement model to study how casing eccentricity and fluid viscosity hierarchy impact the displacement classification. We find that typical field values tend to associate with unsteady displacements, particularly in regions of poor casing centralization, and for displacements involving “traditional” drilling mud, spacer and cement slurry properties. Improving casing centralization, increasing the displacing fluid viscosity and reducing the fluid density difference all act to stabilize the displacement. Similarly, increasing the imposed flow rate can also reduce the rate at which the interface elongates by enhancing the viscous stresses during placement. We compare selected scenarios to displacement simulations performed with the 2-dimensional gap-averaged (2DGA) model, and find qualitative agreement between the 2DGA results and our displacement classification predictions. While our study shows that it is possible to make density-unstable reverse-circulation displacements steady, we note that the identified measures are likely to increase the circulation pressures, which may offset an important benefit of reverse-circulation cementing.
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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 | 0.005 | 0.017 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.006 |
| Scholarly communication | 0.007 | 0.012 |
| Open science | 0.003 | 0.003 |
| Research integrity | 0.007 | 0.004 |
| Insufficient payload (model declined to judge) | 0.017 | 0.013 |
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".