Numerical Modelling of Hydraulic Fracturing in Cohesionless Sand: Validation Against Laboratory Experiments
Bibliographic record
Abstract
Summary In this paper, a new hydraulic-fracturing model is introduced for cohesionless sand, which is also applicable to weak sandstone formations with high permeability and low shear strength. Phenomena such as shear-band development and shear-enhanced permeability are of paramount importance during hydraulic fracturing of cohesionless sand or weak sandstones, which make the fracturing response quite different from what it is conventionally believed to be in competent rocks. The smeared approach in simulating hydraulic fracturing has been implemented in the proposed model within the continuum mechanics framework. Both matrix and fracture flow have been considered in this model. Tensile- and shear-fracture development and their fluid flow were simulated. The cubic law and Touhidi-Baghini’s shear-permeability model (Touhidi-Baghini 1998) were used to capture the permeability evolution and to model flow in tensile and shear fractures, respectively. Shear fracturing of geomaterials involves intense localization of deformation and strain softening, which is a discontinuous phenomenon, resulting in mesh dependency of the results in the continuum model. The fracture-energy-regularization method was used in this model to reduce the mesh-size dependency of the energy dissipated during fracture propagation. The smeared-fracture approach has been validated against laboratory hydraulic-fracturing experiments with reasonable agreement. Consistent with the experiments, the results of the numerical model indicate that tensile fractures are formed in a very small area around the injection point despite the application of high injection pressure compared with the minimum boundary stress. It is found that shear fracturing and shear-permeability evolution are the most important mechanisms that influence and control the fracturing response. The dominant fracturing mechanism is found to be governed by the high permeability and low shear strength of the material.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".