Hydrocarbon breaching of a regional aquitard: The Devonian Ireton Formation, Bashaw area, Alberta, Canada
Bibliographic record
Abstract
Abstract This study is an investigation of aquitard characteristics and hydrocarbon entrapment in the Upper Devonian strata of the Bashaw area of Alberta, Canada. Oil and gas are trapped at two stratigraphic levels, the Leduc-aged Bashaw Reef Complex (D-3) and the Camrose Member–Nisku Formation (D-2), which are separated by a low-permeability aquitard of the Ireton Formation, a marl with variable carbonate content. The Ireton aquitard provides the principal control to cross-formational fluid flow in the area. Over much of the Bashaw Reef Complex, the Ireton aquitard ranges from approximately 25 m (~82 ft) thick to less than 1 m (<3.3 ft) over paleotopographic highs. Associated with thinning is a change in lithofacies and carbonate content from approximately 50% carbonate in the thicker, more basinal facies to more than 80% carbonate and shallower-water facies over the paleotopographic highs of the Leduc. Early replacement dolomitization, probably by density-driven reflux, generated intercrystal porosity on the order of 3 to 4% in the more carbonate-rich facies, which rendered these parts of the aquitard less effective to later hydrocarbon retention. Subsequent differential compaction of the underlying reef complex led to a raised rim morphology and, in places, to a thickness inversion of the Ireton aquitard, that is, a thicker Ireton aquitard draped over the Leduc raised rims. As a result, petroleum migration occurred primarily along the raised rims and was trapped within the present-day highs that are draped by more than 10 m (>32.8 ft) of Ireton aquitard. Where the overlying Ireton aquitard drape is less than 10 m (<32.8 ft) in thickness, breaching and remigration from Leduc traps into the overlying Nisku-Camrose traps may have occurred and/or can be suspected. Invariably, the Ireton aquitard was breached where its carbonate content exceeded approximately 80% and where it is less than 4 m (13.1 ft) thick. The critical controls to hydrocarbon breaching are pervasive dolomitization of the Ireton aquitard with high carbonate content, which enhanced porosity and permeability, and aquitard thickness. Many Nisku and Camrose pools are situated either directly above or updip from such breaches.
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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 | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".