Thermal history and the relationship between diagenesis and the reservoir connectivity: Venture field, offshore Nova Scotia, eastern Canada
Bibliographic record
Abstract
Upper Jurassic and Lower Cretaceous sandstones of the Scotian Basin, offshore eastern Canada, are important gas reservoirs. A study of fluid inclusions related to diagenetic cements provides constraints on the fluid flow history through the rocks. Conventional cores were logged from the Venture B-52, Venture B-13 and Venture H-22 wells. Lithofacies were described and interpreted. Diagenetic minerals including late carbonate cements were analysed from different stratigraphic levels and related to the known reservoir connectivity sequence. A total of 122 primary and secondary fluid inclusions have been analysed from five samples from the Venture B-52, Venture 1, and Venture 4 wells. Homogenisation temperature values in the primary aqueous inclusions hosted in late carbonate cements range from 109 to 135 °C. The values in the earlier quartz overgrowths are slightly lower, ranging from 92 to 121 °C. The ice-melting temperatures from primary inclusions in both quartz overgrowths and late carbonate cements indicate high fluid salinities, between 17 and 20 wt.% NaCl equivalent and 24 to 30 wt.% CaCl equivalent, respectively. Some secondary, predominantly aqueous, inclusions were observed that contain liquid hydrocarbons. They are hosted in detrital quartz, or cross-cut detrital quartz, quartz overgrowths, and late carbonate cements or they occur in microfractures. All have similar homogenization temperatures to primary inclusions, ranging from 82 to 132 °C. However, the melting temperatures range from - 20.2 to 0.8 °C, indicating very dilute fluids with low salinities that range from 4 to 14 wt.% NaCl equivalent. Secondary CO2 inclusions, postdating quartz overgrowths, were found with CO2 melting temperatures indicating the presence of hydrocarbons (avg. - 58 °C) and homogenization temperatures (avg. -10 °C) indicating a relatively high density (i.e., deep trapping depth) carbonic phase. Late carbonate cements are different in the same Industry Sandstone from different wells, indicating that the late carbonate cementation may be at least partly controlled by the reservoir fill and spill sequence, as connected reservoirs show similar late carbonate assemblages. The hydrocarbon migration postdates the late carbonate cementation and the gas reservoir has been charged by aqueous fluids with different salinities during its history. The temperatures determined from Venture samples are higher than present temperatures, implying a thermal maximum at an unknown time in the past. There is no seismic evidence for significant basin inversion in these wells, suggesting the involvement of hot fluids and a higher geothermal gradient than the present ~30 °C/ km.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".