Diagenesis of an evaporite-related carbonate reservoir in deeply buried Cambrian strata, Tarim Basin, northwest China
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Bibliographic record
Abstract
ABSTRACT Many hydrocarbon shows have been reported from potential evaporite-related carbonate reservoirs in the lower to middle Cambrian units in the Tarim Basin. Petrography, facies, and geochemical analyses from outcrop and core samples were integrated to document the effect of diagenetic evolution on these evaporite-related carbonate reservoirs. A simplified depositional model has been developed that reveals a restricted carbonate platform dominated by an evaporatic inner platform lagoon, with shoal and reef facies developed around the platform margins. Grainstones and packstones were deposited at the platform margin and on inner platform shoals, whereas carbonate mudstones and wackestones were deposited in the lagoon associated with evaporites. Early dolomitization and dissolution occurred related to the reflux of evaporated seawater. Breccia-associated fracture porosity caused by a short period of meteoric water-induced dissolution is the predominant type of effective porosity in the anhydrite-bearing dolomudstone reservoir. Thermochemical sulfate reduction (TSR) occurred in the deep subsurface diagenetic environment characterized by high-temperature (100°C–160°C) and high-salinity (16–26 wt. %) aqueous fluid inclusions in TSR calcite that has relatively negative δ13C values (as low as −12‰ Vienna Peedee belemnite) and elevated 87Sr/86Sr values. The porous dolomites contain solution-enlarged pores caused by dissolution of anhydrite and carbonate as a secondary consequence of TSR. This study shows that deeply buried, evaporite-related, ancient carbonate rocks may be effective reservoirs because of a combination of fracture porosity and TSR-induced secondary porosity. Evaporitic Cambrian carbonates buried to over 5000 m (16,500 ft) can thus be considered as targets for future exploration.
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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 | 0.001 | 0.000 |
| 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 | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 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 it