Use of fault-seal analysis in understanding petroleum migration in a complexly faulted anticlinal trap, Columbus Basin, offshore Trinidad
Bibliographic record
Abstract
Abstract In the Columbus Basin, offshore Trinidad, evaluating the controls on fault seal is a prerequisite for understanding how the petroleum fields were charged. In this paper, we present a case study from Mahogany field, where interbedded Pliocene–Pleistocene shales and reservoir sands occur in a broad four-way-closed anticline cut by numerous normal faults. Fault seals in this stratigraphic sequence can be successfully evaluated using shale gouge ratio (SGR), with a transition between sealing and nonsealing faults occurring in the SGR = 0.15–0.25 range. Because of the high net-to-gross ratio of individual sands, low SGR values typically correspond to areas of reservoir self-juxtaposition, whereas good seals (SGR ≳ 0.2) exist where different sands are juxtaposed against one another. The larger structural geometry, which changes significantly from the shallow reservoirs to the deeper ones, closely controls the distribution of stacked, fault-sealed petroleum accumulations in this field. Petroleum column heights in individual fault blocks within the structure are limited either by (1) a cross-fault spill point at a low-SGR window on the west side of a fault block or (2) a synclinal spill point within a fault block from which petroleum leaves the overall four-way closure. The pattern of hydrocarbon-water contacts in the field suggests that petroleum filled and spilled its way from northeast to southwest across the structure with individual sands acting as a separate flow systems. Despite juxtaposition against each other, communication between stratigraphically different sands is minimal. Vertical migration of petroleum along faults is not required to explain the distribution of charged sands, and this is consistent with both petrophysical data and the known sealing character of the faults. This petroleum migration model serves as a tool for evaluating charge risk and column heights in untested fault blocks in the area.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 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) | 0.000 | 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 teacher head, 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".