Origin and evolution of microporosity in packstones and grainstones in a Lower Cretaceous carbonate reservoir, United Arab Emirates
Bibliographic record
Abstract
Abstract Microporosity in carbonate reservoirs is generated by the complex interplay between depositional and diagenetic processes. This petrographical, SEM, fluid-inclusion and isotopic study of a Lower Cretaceous carbonate reservoir, Abu Dhabi, UAE, revealed that: (1) micritization of ooids and skeletal fragments, which resulted in spheroidal (rounded) micrite, accounts for most microporosity in peloidal packstones and grainstones; and (2) transformation of spheroidal micrite into subhedral/euhedral micrite and microspar, known as aggrading neomorphism, could happen via precipitation of syntaxial calcite overgrowths around micrite (micro-overgrowths) and not only, as suggested previously in the literature, by recrystallization involving the dissolution (of micrite) and reprecipitation (of microspar). Precipitation of calcite cement around micrite (i.e. destruction of microporosity) is more extensive in the water zone than in the oil zone, which is possibly contributing to the lower porosity and permeability of the carbonate reservoir in the water zone. Similarity in bulk oxygen isotopic values of micritized packstones and grainstones in the water and oil zones (average δ 18 O V-PDB = −7.2‰ and −7.8‰, respectively) is attributed to: (1) a small difference in temperatures between the crest (oil zone) and the flanks (water zone); and (2) calcite precipitation around micrite occurred prior and subsequent to oil emplacement. Bulk carbon and strontium isotopic compositions of micritized packstones and grainstones in the water and oil zones (average δ 13 C V-PDB = +3.7‰ and average 87 Sr/ 86 Sr ratios = 0.707469) indicate that calcite cement was derived from marine porewaters and/or dissolution of the host limestones. The minimum formation temperatures of bulk micrite/microspar, which are inferred based on paragenetic relationships, fluid-inclusion microthermometry and oxygen isotope data, are around 58–78°C.
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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 | 0.001 |
| 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".