Coupled Modeling of Borehole Instability and Multiphase Flow for Underbalanced Drilling
Bibliographic record
Abstract
Abstract Underbalanced drilling techniques have been applied to avoid or mitigate formation damage, reduce lost circulation risks, and increase the rate of penetration. However, drilling with a bottomhole pressure less than the formation pore pressure will usually increase the risk of borehole instability due to shear or tensile failure of the rock adjacent to the borehole. The extent of rock failure is very sensitive to the pressure in the annulus between the drill pipe, collars or BHA and the formation. The capacity of the drilling fluids to effectively circulate cuttings and cavings to surface is also strongly sensitive to the annular flow velocity. This paper describes the coupling of two popular software packages STABView™ and WELLFLO7™ to solve the complex interaction of borehole instability, rock yielding, collapse, detachment, and wellbore hydraulics during underbalanced drilling operations. In particular, a profile of the average borehole diameter can be predicted that accounts for hole enlargement in weak rock formations, and its consequences for annular pressures and flow velocities. The use of these two models running in a coupled mode is illustrated with two examples. The first one is a case study of a sidetracked well that was drilled underbalanced using coiled tubing technology in western Canada. Severe tight hole problems and poor hole cleaning had been experienced during drilling operations, and ultimately the bottomhole assembly became stuck. Subsequent borehole stability analyses indicated that significant hole enlargement was occurring in two weak shaley intervals. Wellbore hydraulics analyses showed that the liquid velocities achieved in the enlarged intervals of this well were low, which led to an accumulation of cuttings and cavings, thus resulting in the stuck pipe. A second, hypothetical horizontal well case is also described in order to illustrate the procedures for characterizing the operating envelope (i.e., optimal annular pressures and flow rates) prior to drilling an underbalanced well. This example demonstrates additional features of the two software programs for simulating the complexities of hole failure, erosion and enlargement in an annulus with a two-phase fluid for both strong and weak rock cases.
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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".