Development of connected permeability in massive crystalline rocks through hydraulic fracture propagation and shearing accompanying fluid injection
Bibliographic record
Abstract
Abstract The ability to generate deep flow in massive crystalline rocks is governed by the interconnectivity of the fracture network and its permeability, which in turn is largely dependent on the in situ stress field. The increase of stress with depth reduces fracture aperture, leading to a decrease in rock mass permeability. The frequency of natural fractures also decreases with depth, resulting in less connectivity. The permeability of crystalline rocks is typically reduced to about 10−17–10−15 m2 at targeted depths for enhanced geothermal systems (EGS) applications, that is, >3 km. Therefore, fluid injection methods are required to hydraulically fracture the rock and increase its permeability. In the mining sector, fluid injection methods are being investigated to increase rock fragmentation and mitigate high‐stress hazards due to operations moving to unprecedented depths. Here as well, detailed understanding of permeability and its enhancement is required. This paper reports findings from a series of hydromechanically coupled distinct‐element models developed in support of a hydraulic fracture experiment testing hypotheses related to enhanced permeability, increased fragmentation, and modified stress fields. Two principal injection designs are tested as follows: injection of a high flow rate through a narrow‐packed interval and injection of a low flow rate across a wider packed interval. Results show that the development of connected permeability is almost exclusively orthogonal to the minimum principal stress, leading to strongly anisotropic flow. This is because of the stress transfer associated with opening of tensile fractures, which increases the confining stress acting across neighboring natural fractures. This limits the hydraulic response of fractures and the capacity to create symmetric isotropic permeability relative to the injection wellbore. These findings suggest that the development of permeability at depth can be improved by targeting a set of fluid injections through smaller packed intervals instead of a single longer injection in open boreholes.
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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 | 0.000 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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".