Seismic reconstruction of the in situ anisotropic stress field for caprock integrity in the Athabasca oil-sands basin, Canada
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Bibliographic record
Abstract
In the Athabasca Basin of Alberta, Canada, the Lower Cretaceous McMurray Formation reservoir is overlain by the Clearwater Formation, a regionally continuous layer composed predominantly of shales with interbedded mudstones. The shales form the reservoir caprock and have the role of blocking the vertical migration of the steam from thermal oil production by confining the stresses and the deformations. We have developed a new method for the 3D seismic reconstruction of the anisotropic stress field, which accounts for the formation pore pressure and the effective stress. We integrated anisotropy estimated from dipole sonic logs with formation pore pressure data from piezometers and elastic properties obtained from multicomponent seismic inversion. The method combines the Terzaghi effective stress with the Schoenberg and Sayers elastic stiffness matrix for horizontal transversely isotropic (HTI) fractured materials. The key points of this method are the estimation of the formation pore pressure in the abnormal regime of the Clearwater Formation, the normal fracture weakness parameter (based on constraints on the compressional velocity of the intact rock under the HTI assumption), and the 3D seismic anisotropic stress field. We expressed the total vertical stress as the weight of the overlying formations, and the total minimum and maximum horizontal stresses as a combination of the total vertical stress, normal fracture weakness, formation pore pressure, Biot-Willis coefficient, and Lamé elastic constants. The effective principal stresses are estimated from the equivalent total principal stresses and the formation pore pressure multiplied by the Biot-Willis coefficient. We observed excellent consistency between the calculated total minimum horizontal stress and mini-frac values. This new method for the 3D seismic reconstruction of the anisotropic stress field allows for the assessment of the caprock integrity and for operational savings based on a reduced number of mini-frac measurements, and it can be used for time-lapse stress estimation within the thermal production reservoir.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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 it