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TitleIdentifying the source of methane in groundwater in a 'virgin' area with regards to shale gas exploitation: a multi-isotope approach
AuthorBordeleau, G; Rivard, CORCID logo; Lavoie, DORCID logo; Mort, A; Ahad, JORCID logo; Malet, X; Xu, X
Source11th Applied Isotope Geochemistry Conference AIG-11; by Millot, R (ed.); Negrel, P (ed.); Procedia Earth and Planetary Science vol. 13, 2015 p. 219-222, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20140591
PublisherElsevier BV
Meeting11th AIG (Applied Isotopes Geochemistry) Conference; Orléans; FR; September 21-25, 2015
Mediaon-line; digital
File formathtml; pdf
AreaSt. Lawrence Lowlands; St-Edouard
Lat/Long WENS -73.7500 -73.5000 45.2500 45.1667
Subjectsfossil fuels; geochemistry; hydrogeology; Upper Ordovician; methane; shales; gas; isotope geochemistry; groundwater; aquifers; provenance; wells; Utica Shale
ProgramEnvironmental Geoscience, Shale Gas - groundwater
AbstractThe Upper Ordovician Utica Shale located in the St. Lawrence Lowlands (Quebec, Canada) represents a promising reservoir of unconventional gas, which is still 'virgin' with respect to fracking due to a de facto moratorium. A project was initiated in order to evaluate the vulnerability of shallow groundwater resources with respect to potential future activities carried out at depth. The geochemical aspect of the project, relying on isotopes of various compounds from shallow groundwater and rock samples, will allow documenting baseline gas concentrations in the aquifer, evaluating whether gas concentrations and isotopic ratios vary over time, and identifying the source(s) of methane.
Summary(Plain Language Summary, not published)
Geochemical results from the St-Edouard project will be presented at this international conference. Main results are that a series of isotopes must be used in our case to determine the gas source (thermogenic or biogenic) and that methane concentrations in water wells should be monitored over several months before exploration activities begin. Indeed, traditional isotope analyses of methane in groundwater fail to determine the gas origin in this case. Not only that the biogenic methane found seems to have undergone microbial processes, which modifies its isotopic signature and makes it look more and more like a thermogenic source, but thermogenic gas, that is usually found in deep shale units, could come here from units close to the surface since shale units in which water wells were drilled used to be buried ~5 km several million years ago. In addition, methane concentrations vary significantly over time and this could have impact on regulation since a single sampling campaign cannot provide the natural variation range.

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