SUMMARIZATION OF SUBNORMAL PRESSURES AND ACCUMULATION MECHANISMS OF SUBNORMALLY PRESSURED PETROLEUM RESERVOIRS
Bibliographic record
Abstract
The synthesizing of a great number of references on origin of subnormal pressure and underpressured pools demonstraites that two mechanisms are predominantly responsible for subsurface underpressure. The first, probably the most important one, ascribes to erosional rebound; and the second is the effect of hydrostratigraphy and topography. Other causes, such as chemical osmosis and cooling of fluid, seem to play a minor role in underpressure development. Three typical underpressured pools are classified in terms of trap geometry, accumulating mechanism associated with subnormal pressure development. The first type of conventional stratigraphic pools (except lenticular sandstone body) is sealed by low permeability rocks, with little tendency for downdip and edge water to advance, as well as with petroleum charged frequently from downdip source rocks. The second type of isolated lenticular sandstone body reservoirs,abundant in the deepcentral parts of many basins, is characterized with the full presence of oil and gas and absence of water. Several processes, including compacting, hydrofracturing and capillary phenomena prior to uplifterosion, as well as subsequent inwardshale flow driven by erosional rebound, will be able to explain petroleum charged into and water expelled out of isolated porous sandstone bodies. The third type of gas accumulations in lowpermeability reservoirs commonly is located in a basincenter and is downdip from waterbearing rocks. Underpressured gas accumulations evolve from overpressured accumulations due to regional or local structural uplift. Two casestudies, southwestern Alberta Basin and Baise Basin (southwestern China),both experiencing regional structural uplifterosion, indicate that hydrodynamicallyclosed underpressured systems facilitate petroleum accumulation and preservation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.007 | 0.004 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.008 | 0.003 |
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".