Temporal variations of methane concentration and isotopic composition in groundwater of the St. Lawrence Lowlands, eastern Canada
- Geological Survey of Canada (Canada)
- Institut national de la recherche scientifique – Centre Eau Terre Environnement (Canada)
Dissolved methane concentrations in shallow groundwater are known to vary both spatially and temporally. The extent of these variations is poorly documented although this knowledge is critical for distinguishing natural fluctuations from anthropogenic impacts stemming from oil and gas activities. This issue was addressed as part of a groundwater research project aiming to assess the risk of shale gas development for groundwater quality over a 500-km{sup 2} area in the St. Lawrence Lowlands (Quebec, Canada). A specific study was carried out to define the natural variability of methane concentrations and carbon and hydrogen isotope ratios in groundwater, as dissolved methane is naturally ubiquitous in aquifers of this area. Monitoring was carried out over a period of up to 2.5 years in seven monitoring wells. Results showed that for a given well, using the same sampling depth and technique, methane concentrations can vary over time from 2.5 to 6 times relative to the lowest recorded value. Methane isotopic composition, which is a useful tool to distinguish gas origin, was found to be stable for most wells, but varied significantly over time in the two wells where methane concentrations are the lowest. The use of concentration ratios, as well as isotopic composition of methane and dissolved inorganic carbon (DIC), helped unravel the processes responsible for these variations. This study indicates that both methane concentrations and isotopic composition, as well as DIC isotopes, should be regularly monitored over at least 1 year to establish their potential natural variations prior to hydrocarbon development.
- OSTI ID:
- 22780879
- Journal Information:
- Hydrogeology Journal, Journal Name: Hydrogeology Journal Journal Issue: 2 Vol. 26; ISSN 1431-2174
- Country of Publication:
- United States
- Language:
- English
Similar Records
Strike-slip interpretation of basin-bounding faults of the St. Lawrence lowlands basin the Quebec City area, Canada
Gas reservoir potential of the Lower Ordovician Beekmantown Group, Quebec Lowlands, Canada