Diagenesis and Reservoir-Quality Evolution of Incised-Valley Sandstones: Evidence from the Abu Madi Gas Reservoirs (Upper Miocene), the Nile Delta Basin, Egypt
Bibliographic record
Abstract
Abstract Elucidation of the distribution of diagenetic alterations in incised-valley sandstones within a sequence stratigraphic framework allows a better understanding of their reservoir-quality evolution during burial. Gas reservoirs of the upper Miocene Abu Madi Formation (present-day depth ≈ 3350 m, temperature ≈ 116°), the Nile Delta Basin, Egypt, consist of lowstand systems tract (LST) fluvial and transgressive systems tract (TST) estuarine sandstones deposited in an incised valley. These sandstones have a wide range of porosity (2 to 29%) and permeability (0.01 to 6071 mD), which reflect both depositional facies and diagenetic controls. Diagenetic events that influenced the reservoir-quality evolution include mainly the formation of extensive grain-rimming Fe-Mg chlorite, mechanical compaction of ductile grains, pressure dissolution of quartz, and quartz cementation. The chlorite rims, distributions of which are not clearly related to sequence stratigraphy, have preserved reservoir quality by inhibiting quartz cementation but have increased microporosity values in the reservoirs. Calcite cementation (18O = −13.5‰ to −6.0‰, δ13C = −14.3‰ to −1.0‰, and 87Sr/86Sr = 0.707124 to 0.708181), has not influenced the overall reservoir-quality evolution of the sandstones because of its localized occurrence. Other diagenetic events that have little influence on reservoir quality include the more frequent formation of kaolin in the LST fluvial sandstones and formation of pyrite in the TST estuarine sandstones. This study demonstrates the possibility of constraining and evaluating the impact of diagenetic alterations on reservoir-quality evolution in incised-valley deposits and their sequence stratigraphic distribution, and thus has an important impact on hydrocarbon exploration in such settings.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| 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 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".