Coupled Mechanical and Permeability Model for Grain Crushing and Pore Collapse
Bibliographic record
Abstract
ABSTRACT The coupled hydromechanical behavior of porous rocks at high compressive stresses is studied. At such stresses, grain crushing, or pore collapse are the primary failure modes. The need to study and model such behaviors is necessary as exploitation of reservoirs reaches depths where stress regimes for such failures are becoming relevant. Experimental data from triaxial compression and Ko tests at different stress ratios are analyzed to model the effects of grain crushing or pore collapse on the stress-strain behavior but also on the changes in the permeability. A stress-dependent permeability model is developed to account for the large drops in permeability associated with these compaction failures. The permeability model modifies the Kozeny-Carman model for permeability as a function porosity to include a stress dependent term linked to grain crushing or pore collapse. Comparison with the experimental results show the validity of the model in capturing permeability changes during compaction failure. INTRODUCTION Reservoir rocks are sometimes loaded at high compressive mean stress at deep reservoirs and high depletions. Moreover, proppant or other completions that support the face of boreholes or perforations may result in both high deviatoric and high mean stresses. Such loadings can lead to grain crushing and/or pore collapse of reservoir rocks. Sandstones often experience grain crushing at high mean stresses. A combination of deviatoric and hydrostatic loading facilitates this phenomenon (Papamichos et al. 1993). High porosity chalks on the other hand experience pore collapse where the open skeleton structure of the material breaks, and destructures giving a sharp decline in porosity (e.g., Papamichos et al. 1997). Both phenomena cause fundamental changes in the structure of the rock, the pore space and thus significantly affect the rock permeability. This work proposes a permeability model that is linked to the mechanical failure of the rock due to pore collapse and grain crushing and attempts to simulate the sharp permeability decline observed during grain crushing and pore collapse and which cannot be captured with only porosity dependent permeability models løike the Kozeny-Carman. Experiments are presented for two sandstones and a chalk where these phenomena had been investigated to a certain extent. Based on the experimental results a model was advanced that appears to provide reasonable simulations of the experimental results.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
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".