| Title | Temporal variations of methane concentration and isotopic composition in groundwater of the St. Lawrence Lowlands, eastern Canada |
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| Author | Rivard, C ;
Bordeleau, G; Lavoie, D; Lefebvre, R; Malet, X |
| Source | Hydrogeology Journal vol. 26, issue 2, 2017 p. 533-551, https://doi.org/10.1007/s10040-017-1677-y  Open Access |
| Year | 2017 |
| Alt Series | Natural Resources Canada, Contribution Series 20170257 |
| Publisher | Springer Nature |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Province | Quebec |
| NTS | 21L/12 |
| Area | Saint-Édouard; Lotbinière |
| Lat/Long WENS | -72.0000 -71.5000 46.7500 46.5000 |
| Subjects | fossil fuels; hydrogeology; environmental geology; geochemistry; Nature and Environment; Science and Technology; groundwater resources; groundwater geochemistry; groundwater pollution; water quality;
petroleum resources; hydrocarbon recovery; hydrocarbons; gas; bedrock geology; lithology; sedimentary rocks; shales; clastics; carbonates; methane; hydrocarbon migration; stable isotope studies; carbon isotopes; hydrogen isotopes; isotope ratios;
observation wells; gas wells; water wells; carbon geochemistry; organic carbon; St. Lawrence Lowlands; Talisman A267 Well; Talisman A275 Well; Lorraine Group; Nicolet Formation; Utica Shale; Sainte-Rosalie Group; Lotbinière Formation; Les Fonds
Formation; monitoring; Phanerozoic; Paleozoic; Ordovician |
| Illustrations | location maps; geoscientific sketch maps; stratigraphic charts; cross-sections; tables; time series; plots |
| Program | Environmental Geoscience Shale Gas - groundwater |
| Released | 2017 11 10 |
| Abstract | 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-km2 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 2.5Êyears 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 1Êyear to establish their potential natural variations prior to hydrocarbon development. |
| Summary | (Plain Language Summary, not published)
Dissolved methane concentrations in shallow groundwater are known to vary both spatially and temporally. However, the extent of these variations is
poorly documented and this knowledge is critical for distinguishing natural fluctuations from anthropogenic impacts stemming from deep industrial activities. A groundwater study was carried out over a 500 km2 area in the St-Édouard region, located in
the St. Lawrence Lowlands. The St. Lawrence Lowlands were the target of shale gas exploration between 2006 and 2010, before a moratorium was imposed. Results showed that methane concentrations can vary over time from 2.5 to 6 times the smallest
recorded value. Methane isotopes, which are a useful tool to distinguish the gas origin, were found to be stable for most wells, but they varied significantly over time in the two wells where methane concentrations are the lowest. This indicates that
both methane concentrations and isotopes should be regularly monitored over at least one year to get a grasp on the potential natural variations prior to any hydrocarbon activity. |
| GEOSCAN ID | 310587 |
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