Vadose Zone Gas Migration and Surface Effluxes after a Controlled Natural Gas Release into an Unconfined Shallow Aquifer
Bibliographic record
Abstract
Core Ideas Subsurface gas migration results in localized surficial CH 4 releases. Surficial CH 4 emissions show pronounced temporal variations. Methane concentrations in soil gas exceed lower explosive limits at low leakage rates. Increasing CO 2 effluxes and stable C isotope signatures indicate vadose zone CH 4 oxidation. Instantaneous surficial effluxes do not indicate the magnitude of subsurface gas leakage rates. Shale gas development has led to concerns regarding fugitive CH 4 migration in the subsurface and emissions to the atmosphere. However, few studies have characterized CH 4 migration mechanisms and fate related to fugitive gas releases from oil or gas wells. This paper presents results from vadose zone gas and surface efflux monitoring during a natural gas release experiment at Canadian Forces Base Borden, Alliston, Ontario, Canada. Over 72 d, 51 m 3 of natural gas (>93% CH 4 ) was injected into a shallow, unconfined sand aquifer at depths of 4.5 and 9 m. Methane and CO 2 effluxes in combination with soil gas concentrations and stable C isotopic signatures were used to quantify the spatiotemporal migration and fate of injected gas. Preferential gas migration pathways led to vadose zone hot spots, with CH 4 concentrations exceeding the lower explosive limit (5% v/v). From these hot spots, episodic surface CH 4 effluxes (temporally exceeding 2500 μmol m −2 s −1 [3465 g m −2 d −1 ]) occurred during active injection. Higher injection rates led to increased average CH 4 effluxes and greater lateral migration, as evidenced by a growing emission area approaching 25 m 2 for the highest injection rate. Reactive transport modeling showed that high CH 4 fluxes resulted in advection‐dominated migration and limited CH 4 oxidation, whereas lower CH 4 effluxes were diffusion dominated with substantial CH 4 oxidation. These results and our interpretations allowed us to develop a conceptual model of fugitive CH 4 migration from the vadose zone to the ground surface.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".