Underbalanced Perforation and Completion of a Long Horizontal Well: A Case History
Bibliographic record
Abstract
Abstract A clastic reservoir in central Oman is to be developed with some 100 wells. The rock is sensitive to formation damage and experience shows that productivity is improved by a factor of 10 by perforating with deep-penetrating charges underbalanced and avoiding contact of brine with the formation. The wells will be horizontal to drain a 24.5m oil rim, and zonal isolation for future water and gas shutoff is desirable. An interval of 600 meters was perforated with 4 ½" OD guns. The guns were retrieved under pressure and a lower completion packer was run to isolate the reservoir from the surface. The upper completion was run with crude in the hole to ensure that no brine should contact the formation. To perforate underbalanced with a drilling rig, the well was constructed with a 7" liner at the start of the build section to total depth of the well. A 7" tie-back was run with a surface controlled downhole isolation valve (DHIV) as a barrier after perforating. The well was displaced to crude to create underbalance. A 7" predrilled liner joint was run beneath the DHIV in the work string to allow circulating out well bore fluids so that the guns could be retrieved safely. A rotating control head and underbalanced drilling surface equipment package was utilized for stripping with 8,000 kPa surface pressure bleed off volumes for tripping and manage the crude circulating system. The tie-back was retrieved and the upper completion was run after setting a plugged packer in the 7" liner. This method is unique because it utilized a conventional drilling rig for completion operations along with an underbalanced drilling package to perforate and complete the well underbalanced.
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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 | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.003 | 0.002 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.004 | 0.003 |
| Science and technology studies | 0.004 | 0.003 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.007 | 0.007 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
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".