Severe wellbore instability in a complex lithology formation necessitating casing while drilling and continuous circulation system
Bibliographic record
Abstract
Abstract Most of drilling hole problems are attributed to wellbore stability issues which adversely cause excessive lost time and cost millions of dollars. The past drilling experiences in Kupal oilfield showed excessive mud losses, kick flows, tight holes and pipe stuck leading to repeated reaming, fishing and sidetracking. Most of the drilling-associated problems in this field occurred during drilling the 12 ¼-in. hole, which is across the non-reservoir Gachsaran formation (consisting of anhydrite, gypsum and marl with thin limestone layers). Mainly due to the lack of required formation evaluation data, no geomechanical studies of this formation have been conducted to date. In this work, first, we constructed a geomechanical model to investigate the root of the problems. This is a pioneer wellbore stability work for such a complex lithology formation which included finding the equations best-matching with core data and field observations. Finally, to overcome the field challenges and hole problems, the study proposes some field remedial actions. The results of the geomechanical modeling show that the pore pressure, shear and tensile failure gradients are greatly variable with the safe mud weight window becoming excessively narrow at some intervals. This accounts for the encountered wellbore stability issues as managing the mud weight in these situations requires several casing strings. To mitigate the extent of the problem, this study proposes the application of innovative drilling technologies including casing while drilling to eliminate the casing running time with potential reduction in drilling time, and continuous circulation system to prevent cuttings settling and kick flows during connections. These technologies are capable of elimination of the geomechanical part of the drilling delay (30% of the average 77 drilling days) per well.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".