Characteristics of the Shale Gas Reservoir Rocks in the Lower Silurian Longmaxi Formation, East Sichuan Basin, China
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Bibliographic record
Abstract
The Sichuan basin is an oil-bearing and gas-rich basin with extensive development of the Lower Silurian Longmaxi Formation shale in southwestern China. The gas shows in the shale were identified in exploration wells mainly located between southeastern Sichuan basin and Western Hubei-Eastern Chongqing. The thickness of the Lower Silurian Longmaxi Formation shale ranges from 65 to 516 m. The base of the Longmaxi Formation shale is graptolite-rich transgressive black shale. Its thickness increases eastward in the study area, similarly as the sand content in the formation, with the latter also increasing stratigraphically upward. The Longmaxi Formation is comprised by eight lithofacies, including laminated and nonlaminated mudstone/shale, dolomitic siltstone, laminated lime mudstone/shale, argillaceous siltstone, laminated and nonlaminated silty mudstone/shale, fine grained silty sandstone, calcareous concretions and nonlaminated shale enriched organic matter. The biota in the formation is dominated by graptolites, ostracods, echinoderms, brachiopods, trilobites and radiolarian. Longmaxi Formation contains 0.2% to 6.7% of organic carbon ( TOC). The organic matter is overmature, with Ro 2.4%−3.6% and dominated by Type II-kerogen. Quartz silt, which is the second important component of the shale gas reservoir quality, occurs as laminae and/or disseminated and varies from 2% – 93% in the shale. The size of quartz silt ranges from 0.03 to 0.05mm, with terrigenous origin. Porosity measured on the core samples of the shale from the Longmaxi Formation in exploratory wells ranges from 0.58% to 0.67%. The microporosity observed in the thin sections of the shale is about 2%, and dominated by the intercrystal and intragranular pores, with the pore size ranging from 100nm to 50μm. The other pore types are related to fractures, with the width of ranging from 2 to 5μm. The formation mechanism of the shale reservoir rocks includes favorable mineral composition, diagenesis and thermal cracking of organic component. There are some differences between Longmaxi Formation shale and Barnett shale in USA. The former is buried deeper, higher degree of thermal evolution, lower gas content, denser, more quartz of terrigenous origin. The prevailing low content of organic matter and highly variable quartz content in the Longmaxi Formation shale suggests there are only marginal conditions for exploration of shale gas resource. However, the high variability in both the content of TOC and quartz in the shale indicates that locally, particularly in the southeastern part of the basin, favorable conditions for shale gas may have developed. More detailed paleogeographic, burial history, gas content and quartz origin studies are needed to better access shale-gas potential of the Lower Silurian Longmaxi Formation shale.
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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 | 0.000 | 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 | 0.002 |
| 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 it