Off-Bottom Plug Placement: On the Effects of Pulling Out of the Hole
Bibliographic record
Abstract
Abstract Several cement plugs are often placed along cased oil and gas wells, commonly using the balanced-plug technique, to ensure proper abandonment. The placement process starts with the injection of cement slurry into wells that are otherwise filled with lighter wellbore fluids. The injector is pulled out of the hole when the cement slurry is levelled in the injection tube and the annular space between the injector and casing walls (from hereon referred to as POOH). Successful placement is achieved if the plug remains in place after the POOH. In our previous works, we investigated the hydrodynamics of the early stages of the balanced-plug method and provided a mechanistic description of the events that would lead to the accumulation of the injected fluid. In this work, we focus on the hydrodynamics of the final stage of the balanced-plug method. We study the impact of POOH on the lower interface of the injected cement layer. We develop a two-dimensional (2D) model that is representative of the process and conduct numerical simulations, using OpenFOAM, to explore the deformation of the lower interface of the cement plug at different POOH velocities and for different distances between the injector tip and the lower interface of the cement plug. We show that the injector pullout creates vortices at the injector tip, leaving a trail of vortices within the viscoplastic layer as the injector is pulled away from the interface. Our preliminary results suggest that the interface evolves approximately independently of the injector pullout when the initial distance between the injector and the bottom interface of the cement plug is sufficiently large. Here, the development of instabilities at the interface is reminiscent of the Rayleigh-Taylor instability (RTI) irrespective of the pullout velocity. We show, however, that the injector pullout promotes the mixing of fluids when the interface is close to the injector initially. Reduced POOH velocity appears to enhance the mixing close to the interface.
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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 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| 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".