Predicting the potential for induced earthquakes due to long term oil/gas production in the Niger Delta basin, Nigeria
Bibliographic record
Abstract
Production induced reservoir pressure dissipation causes stress changes leading to reduction in magnitude and rotation of the horizontal stresses on fault planes. Abrupt, stick-slip and spontaneous shear displacement of the downthrown block on crustal faults which can be due to stress perturbations is the causative mechanism of induced earthquakes in energy production. In this studies, production induced depletion has been estimated as percentage of predicted reservoir pore pressure at the well-fault plane interface in a horizon interval of 3500 – 3980m. The structural attitudes of three representative fault planes were also measured from depth structure map and dynamically derived in situ stresses determined. Fault reactivation tendency was assessed based on the Coulomb - Mohr and composite Coulomb - Griffiths fault strength criteria to determine the optimal window for critically stressed and optimally oriented faults for slippage. The static frictional coefficient of the reservoir bounding faults vary from 0.43 – 0.46, phyllosilicate cataclastic infilling suspected for the low values. The horizontal stress orientation rotated through 3.20 to 17.50 causing the new orientation of the maximum horizontal stress to rotate through 108.220 to 122.50 and the minimum horizontal stress rotated through 18.220 at 10% to 32.50 at 99% reservoir pressure dissipation on the frictionally unstable fault plane 1. The magnitude of the maximum horizontal stress reduced from 51.2mPa to 41.5mPa and minimum horizontal stress from 36.1mPa to 26.0mPa at 99% reservoir pressure depletion. Predicted potential for induced earthquakes increased with depletion as the optimal fault reactivation window widened from 78.10 and 36.10 under in situ conditions to 77.10 and 37.50 for all steeply dipping faults with poles within the window and parallel to the maximum horizontal stress to reactivate and generate felt seismicity. A wider window at full reservoir depletion imply possibility of increased number of faults and their potential risk of slippage. Injection in water flooding operations to maintain reservoir pressure as well as enhance hydrocarbon recovery is recommended.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".