Diagenesis and Reservoir Evolution of Low Permeability Sandstones: A Case Study of the Second Member of the Jurassic Sangonghe Formation, Central Junggar Basin, China
Bibliographic record
Abstract
ABSTRACT The low‐permeability oil‐bearing tuffaceous sandstones of the second member of the lower Jurassic Sangonghe Formation (J 1 s 2 ) in the Well Pen‐1 west sag of the central Junggar Basin occur in a deep burial setting (> 4000 m). They contain abundant oil and gas shows and hold promising exploration prospects. However, the reservoir heterogeneity is strong due to complex lithofacies and diagenesis, leading to significant productivity differences between adjacent wells. Therefore, identifying the lithofacies and diagenesis of the J 1 s 2 sandstones and elucidating their influence on the evolution of relatively high‐quality reservoirs is of utmost importance for oil and gas exploration and development in this area. Samples from the Well Pen‐1 west sag, representing the J 1 s 2 sandstones, were investigated utilising core and thin section observations, scanning electron microscopy, X‐ray diffraction, fluid inclusions and carbon and oxygen isotope analyses. The J 1 s 2 sandstones are mainly medium‐ to fine‐grained and moderate‐ to‐well‐sorted feldspathic litharenites and litharenites. The tuffaceous contents range from 2.6% to 25% and the authigenic clay contents, produced by diagenesis, range from 0.6% to 12%, although carbonate cements are not abundant (av. 3.1%). Four sandstone lithofacies have been identified based on mineral compositions, leading to variations in diagenetic evolution and reservoir quality. Early diagenetic events included compaction, alteration of tuffaceous matrix and feldspar, and development of smectite, chlorite, kaolinite and early calcite. Mesogenic alteration included feldspar and tuffaceous matrix dissolution, alteration of kaolinite, chlorite and illite, and precipitation of quartz, anhydrite, late calcite and ferrocalcite. The alteration of the tuffaceous matrix resulted in a complex pore‐throat structure in the J 1 s 2 sandstones. The pebbly sandstone and conglomerate (SC) and fine‐grained sandstone (Sm) lithofacies are generally characterised by high compaction resistance, low tuffaceous matrix and cement contents, and abundant secondary dissolution pores, and they exhibit better reservoir quality and great potential for oil and gas enrichment.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| 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 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".