Near-Surface External-Casing Corrosion in Alaska: Cause and Mitigation
Bibliographic record
Abstract
Summary Recently, a number of external-casing failures on a group of relatively new wells in the Kuparuk field of Alaska prompted an investigation into the cause. The investigation determined that external surface-casing-corrosion failures had occurred near the top of the casing cement within the conductor. The surface-casing corrosion was found to be caused by repetitive events of surface water entering into the top of the annulus between the surface casing and the conductor above the primary cement top. Testing of water and cement samples taken from the field indicates that the addition of oxygenated water and chemical salts that leach from the cement creates a low-resistance electrolyte resulting in an extremely corrosive environment. The yearly replenishment of oxygenated water in this environment sets up an electrochemical cell that corrodes the surface casing. Elevated casing temperatures (≈125°F) accelerate the corrosion rates and increase the temperature gradient between the casing and the conductor, creating a thermogalvanic-corrosion cell. Although damaged surface casing has been repaired mechanically on numerous wells by excavation and installation of welded sleeve patches, accessing the damaged surface casing can be difficult. Inhibiting the corrosion mechanism is considered a more tenable solution. This paper will Provide an outline of the extent of shallow external-casing corrosion seen in the field. Detail the mechanisms for the external corrosion. Detail the mechanical-repair procedures used to return the wells to service. Discuss possible mitigation methods to inhibit corrosion on existing wells. Discuss the treatment chosen to stop the corrosion. Provide details of treatments used to inhibit further shallowcasing corrosion.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".