Researchers from Canadian universities study a controlled natural gas release on groundwater.
Methane leakage from imperfectly sealed well bores on unconventional shale gas wells has been a concern regarding environmental impacts to the groundwater resources. Studies on methane release in the atmosphere appear more often than controlled studies of subsurface methane release and its effects on groundwater. Little study has been done on fugitive gas migration, subsurface source identification and oxidation potential in groundwater. One such study was performed by Canadian University professors at the Borden Research Aquifer, where varying amounts of methane were injected into a shallow freshwater aquifer at different depths over a period of 72 days, trying to find answers to questions such as: How mobile and what controls fugitive methane in groundwater? Does methane persist or degrade in groundwater after leakage is stopped? How best can fugitive methane be detected in groundwater, and how accurate are tracer techniques currently used? Movement and measurements of methane were taken over a period of close to a year.
The study looked at methane injection phases and rates, depths, sediment composition, and monitoring and sampling analysis. Initial conclusions from this controlled natural gas release research indicate:
- Fugitive gas depicting an active leakage, is very mobile and tends to migrate laterally in plumes.
- Gas migration and groundwater are controlled by geological characteristics, which can result in trapping and diverting gas laterally and upward.
- Groundwater impacts are exacerbated for a defined time, and, as pressure is lost, balance between gas and water is enhanced after injection period.
- There was little or no sign of microbially mediated degradation of methane over the 323 day study.
- Observations made are in line with other studies in the Borden aquifer, demonstrating groundwater quality impacts from non-aqueous phase fluids are varied at the pore scale level, but in a general behavior, are more insightful, predictable, and monitorable using high state science knowledge and technologies.
- Fugitive gas assessment in groundwater can be monitored using systems specific to the site, with attention to the presence and nature of potential gas barriers or traps.
- Isotopic tracer techniques may not be the best for measuring methane when levels are less than 2 mg/L and sparsely located.