Research on the micro-pore structure and multiscale fractal characteristics of shale under supercritical CO2 action: A case study of the Chang 73 submember in the Ordos Basin, China
Bibliographic record
Abstract
To elucidate the mechanism of supercritical CO 2 (ScCO 2 ) on the microporous structure of shale, this study focuses on the Chang 7 3 submember of the Yanchang Formation in the Ordos Basin. Utilizing a combination of organic geochemical and mineral composition analyses, low-temperature gas (CO 2 and N 2 ) adsorption experiments and nuclear magnetic resonance (NMR) scanning methods are employed—combined with multiscale fractal theory—the research comprehensively analyze the changes in shale microporous structure and its fractal characteristics under ScCO 2 treatment. The results show that after ScCO 2 treatment, the total organic carbon (TOC) content of the shale samples decreases, the quartz content increases, while the contents of clay minerals and feldspar decrease. Notably, TOC and mineral components are more sensitive to pressure changes compared to temperature variations. Additionally, shale pores are mainly distributed in the micropore (0–2 nm) and mesopore (2–50 nm) ranges, contributing significantly to the specific surface area, while macropores (>50 nm), though fewer, considerably contribute to the total pore volume. Following ScCO 2 treatment, the total specific surface area of shale samples decreases, whereas total pore volume, average pore diameter, and effective porosity increase. Specifically, total specific surface area and average pore diameter are more sensitive to temperature, while total pore volume and effective porosity are more influenced by pressure. The shale pores exhibit multi-scale fractal characteristics, with micropores displaying higher fractal dimensions than meso- and macropores. After ScCO 2 treatment, fractal dimensions at all scales decline, indicating an improvement in the complexity of the shale pore structure. A significant positive correlation exists between the fractal dimension of micropores and TOC content, whereas meso- and macropore fractal dimensions have a stronger correlation with quartz and clay mineral content. These findings indicate that changes in shale mineral characteristics are intrinsic factors affecting microporous structure, while ScCO 2 treatment conditions are important external factors. The interaction of both determines the evolution of shale pore structures, providing a valuable scientific basis and practical guidance for the optimal selection of carbon capture, utilization, and storage (CCUS) target layers.
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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 | 0.001 |
| 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".