Dépôt numérique

Spatial distribution of natural gas concentrations and isotopic signature in shallow aquifers of the St.Lawrence Lowlands(Québec, Canada).

Barnetche, Diogo; Pinti, Daniele Luigi; Larocque, Marie; Gélinas, Yves; Lefebvre, René; Hélie, Jean-François; Moritz, Anja; Beaudry, Châtelaine et Retailleau, Sophie (2013). Spatial distribution of natural gas concentrations and isotopic signature in shallow aquifers of the St.Lawrence Lowlands(Québec, Canada). In: 66th Canadian Geotechnical Conference and the 11th Joint CGS/IAH-CNC Groundwater Conference - GéoMontréal 2013, 29 septembre-3 octobre 2013, Montréal, Canada.

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An academic consortium from UQAM, Geotop, Concordia University, INRS-ETE and Laval University has initiated a study as part of the strategic environmental assessment of shale gas production from the Utica Shale in the St. Lawrence Lowlands. The objective of the study is to contribute objective data on 1) the presence of light hydrocarbons (methane and alkanes) in groundwater, 2) the origin of these hydrocarbons (bio- or thermogenic), and 3) migration mechanisms of these gases through gas well casings. These data will be provided through geochemical and numerical modeling methods. Here we will focus on the first two objectives of the project, whereas the study related to the third objective is the object of another communication at this conference (Nowanooz et al.). Over a hundred private and public wells were sampled in 2012 south of the St. Lawrence River between Montreal and Quebec City. The area corresponds to the most prospective corridor for Utica shale gas production, which is where several vertical and horizontal exploration wells have been drilled, some of which were fracked. The area includes the Richelieu, Yamaska, Nicolet, Saint-François and Bécancour River basins, between the piedmont of the Appalachians and the St. Lawrence River. Water was analyzed for light n-alkane concentrations (CH4, C2H6 and C3H8) and carbon isotopic composition (d13C) as well a for noble gas isotope ratios (4He, 40Ar and 222Rn). Methane isotopic composition is useful to distinguish biogenic methane produced within the Quaternary deposits from thermogenic methane originating from the deeper Lorraine or the Utica shales. To distinguish between the two shale formations, the d13C values of heavier alkanes (C2H6 and C3H8) are also measured to quantify the isotopic rollover (heavier gases show lighter d13C values) observed in this area as in other shale gas production regions. Noble gases, particularly 4He, are useful tracers of gas migration and cross-formational fluid flow. 222Rn is a radioactive element of the U-decay chain useful to discriminate between local sources of radiogenic 4He from deeper sources (for which Rn and He should be decoupled). In this communication, the strategies used for this environmental study are presented along with results on the spatial distribution of hydrocarbons and associated noble gases in the region, which will be detailed in two other communications in this conference (Moritz et al.; Pinti et al.).

Type de document: Document issu d'une conférence ou d'un atelier
Mots-clés libres: methane; alkanes; radon; noble gas; shale gas; dissolved gas; groundwater; isotopic signature
Centre: Centre Eau Terre Environnement
Date de dépôt: 10 mai 2018 18:09
Dernière modification: 10 mai 2018 18:09
URI: https://espace.inrs.ca/id/eprint/4151

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