The effect of pore pressure depletion and injection cycles on ultrasonic velocity and quality factor in a quartz sandstone
Bibliographic record
Abstract
Abstract Passing seismic waves generate transient pore-pressure changes that influence the velocity and attenuation characteristics of porous rocks. Compressional ultrasonic wave velocities Vp and quality factors Qp in a quartz sandstone were measured under cycled pore pressure and uniaxial strain conditions during a laboratory simulated injection and depletion process. The objectives were to study the influence of cyclical loading on the acoustic characteristics of a reservoir sandstone and to evaluate the potential to estimate pore-fluid pressure from acoustic measurements. The values of Vp and Qp were confirmed to increase with effective stress increase, but it was also observed that Vp and Qp increased with increasing pore pressure at constant effective stress. The effective stress coefficient n was found to be less thanone and dependent on the pore pressure, confining stress, and load. At low pore pressures, n approached one and reduced nonlinearly at high pore pressures. The change in Vp and Qp with respect to pore pressure was more pronounced at low versus high pore pressures. However, the Vp variation with pore pressure followed a three-parameter exponential rise to a maximum limit whereas Qp had no clear limit and followed a two-parameter exponential growth. Axial strain measurements during the pore-pressure depletion and injection cycles indicated progressive viscoelastic deformation in the rock. This resulted in an increased influence on Vp and Qp with increasing pore-pressure cycling. The value Qp was more sensitive in responding to the loading cycle and changes in pore pressures than Vp; thus, Qp may be a better indicator for time-lapse reservoir monitoring than Vp. However, under the experimental conditions, Qp was unstable and difficult to measure at low effective stress.
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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 | 0.001 | 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 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".