Wellbore Stability Considerations for Drilling High-Angle Wells Through Finely Laminated Shale: A Case Study From Terra Nova
Bibliographic record
Abstract
Abstract High angle wells drilled into finely laminated shale are often found to be less stable than comparable wells drilled into non-laminated rock. This can be attributed to a variety of factors including, but not limited to, well trajectory, the in-situ stress field, rock strength anisotropy, shale reactivity issues, chemical imbalances between the drilling fluid and shale pore fluid, and many others. However, due to the lack of available data some of these mechanisms are difficult to quantify and therefore are typically not accounted for during well planning. This can result in significant wellbore instability issues that substantially elevate drilling operation costs. In this paper, a comprehensive approach to account for many of these wellbore instability mechanisms is outlined. A plane-of-weakness model is utilized to account for the effects of weak bedding planes and other discontinuities. The model uses parameters that are obtained by curve fitting triaxial strength test results conducted at various angles with respect to bedding. Additionally, traditional mechanical and chemical effects were also addressed and incorporated into the pre-drill model to assist in well planning. The model was then implemented at the Terra Nova field for the case of a highly deviated wellbore drilled through finely laminated shale nearly parallel to bedding. Real-time monitoring of measurement and logging while drilling data was key to identifying the unstable sections so that the root cause of instability could be diagnosed. The appropriate remedial action was then applied and wellbore instability problems were mitigated. Both mechanical and chemical borehole instability models were applied in a case history to evaluate the potential for wellbore instability. In particular, bedding-plane related and chemically-induced instability were addressed and overcome through comprehensive modeling and the deployment of modified operational procedures.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".