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 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 | 0.000 |
| 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 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".