Origin of giant Ordovician cavern reservoirs in the Halahatang oil field in the Tarim Basin, northwestern China
Bibliographic record
Abstract
Abstract Cavern and vug porosities in the Ordovician carbonates in the Halahatang oil field are currently hot targets for hydrocarbon exploration in the Tarim Basin of northwestern China. However, crucially, the formation of cavern and vuggy porosities have not been fully understood due to multiphase tectonic-driven (e.g., faults, unconformities) diagenetic alterations. Here, we integrated petrology observations and geochemical analyses (C, O, Sr isotopes, trace and rare earth elements [REE], clumped isotopes, and laser-based U-Pb dating), aiming at determining the timing for tectonic-driven calcite precipitation, which is closely tied to karstic reservoir development. Vug-filling calcites were emplaced in the late Caledonian (460.8 ± 3.4 and 448.6 ± 5.3 Ma) and early Hercynian (335 ± 19 Ma), and the U-Pb ages for fracture-filling (ca. 364 ± 53 and 282.9 ± 5.4 Ma) and megacrystalline (from 324 ± 23 to 300.9 ± 4.8 Ma and 244.13 ± 13 to 240.5 ± 4.1 Ma) calcites predominantly fell within the Hercynian. In addition, the latest fracture-filling calcites show a slightly younger U-Pb age of ca. 158 ± 17 Ma. The combination of other geochemical analysis, including clumped isotopes, δ13C, δ18O, and 87Sr/86Sr isotopes, REE, and fluid δ18O calculation, suggest that these calcites were precipitated from formation fluids substantially influenced by meteoric water along with alternative hydrothermal fluid. Hence, this study emphasizes that fracture-related cavern reservoirs of the Halahatang oil field were well correlated with the early Hercynian, late Hercynian, and Yanshanian tectonic events and their associated fluids mixing activity. The methodologies and outcomes from the present study may be able to guide future hydrocarbon exploration in the Halahatang oil field and be applied to other oil fields with similar tectonic backgrounds.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".