Sedimentary facies and reservoir characteristics of the Western Sulige field Permian He 8 tight sandstones, Ordos Basin, China
Bibliographic record
Abstract
The He 8 sandstone unit in the Western Sulige field is one of the most prolific gas‐producing intervals in the Ordos Basin. Sedimentologic and reservoir characteristics analysis were conducted to investigate the reservoir's petrological, diagenetic, petrophysical properties, and production characteristics. Three sandstone types and four lithofacies were identified. The two most commonly observed lithofacies are labelled lithofacies C and D. Lithofacies C is composed of fine‐ to medium‐grained litharenites (Sandstone I); lithofacies D includes coarse‐grained sublitharenites (Sandstone II) and coarse‐grained/gravelly litharenites (Sandstone III). Compared with Lithofacies C, Lithofacies D was deposited as a series of laminated sand sheets in a higher energy fluvial system. The tightness of Sandstone I is a result of an episode of intense compaction of the rock framework causing early‐diagenetic dissolution of grains and deformation of ductile rock fragments. The processes that led to the low permeability of Sandstone II and Sandstone III are more complex. In addition to intense compaction, the growth and emplacement of quartz and clay cements are a critical factor. Diagenesis and porosity evolution analysis show that the petrophysical properties of these sandstones were better at the gas charging time. The porosity and permeability values of Sandstones II and III are similar at surface, but significantly different at formation pressure. This leads to differences in gas production rates. Sandstone II has higher gas production rates and cumulative gas production than Sandstone III. The presence or absence of Sandstone II controls the distribution of sweet spots within less productive tight gas reservoirs.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 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".