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TitreMethane variations in groundwater
AuteurRivard, C; Bordeleau, G; Lavoie, D; Lefebvre, R; Malet, X; Ahad, J
SourceAmerican Association of Petroleum Geologists, Annual Meeting Abstracts .
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160261
ÉditeurAmerican Association of Petroleum Geologists (AAPG)
RéunionAmerican Association of Petroleum Geologists (AAPG) Annual Convention & Exhibition 2017 (ACE2017); Houston, TX; US; avril 2-5, 2017
Documentpublication en série
Sujetsméthane; gaz; eau souterraine; hydrocarbures; schistes; effets sur l'environnement; combustibles fossiles; hydrogéologie; sédimentologie
ProgrammeGas de schiste - sismicité, Géosciences de l'environnement
Résumé(disponible en anglais seulement)
Methane and other dissolved gas concentrations in groundwater not only vary spatially for a given region, they also vary both over time and with the sampling technique at a given location. However, very few studies have monitored these variations. A project was conducted in southern Quebec to study potential impacts of hydrocarbon development on groundwater and these issues were also addressed. The study area is located in the St. Lawrence Lowlands, where the Utica Shale was the target of exploration between 2006 and 2010, until a de facto moratorium came into force.
Variations in dissolved alkane concentrations and methane isotopic signature have been monitored in two residential wells and five shallow observation wells drilled for this project (50 to 150 m in depth). Different techniques were also used to sample groundwater in ten wells to compare their results: two types of low flow rate submersible pumps (Redi-Flo2 and bladder) and HydraSleeve bags before and after pumping.
Groundwater methane concentrations in this region vary from below detection limit to supersaturated. Monitoring showed that natural methane fluctuations over time vary from 1.6 to 4.7 times the smallest recorded value for a given well, sampling depth and sampling technique. The different sampling techniques showed that: 1) the type of pump used does not seem to have a significant effect on concentrations, as long as the tubing has the same diameter and 2) HydraSleeve bags do not provide consistent results compared to the other two methods. Results for HydraSleeve bags before or after pumping can either be higher or lower than any other method, by up to 3.5 times, likely because some water exchange can occur as the bag is pulled up. However, the methane isotopic signature is much less variable. This study confirms that carrying out a single baseline study solely using methane concentrations does not provide an accurate picture of the pre-development environment that could serve to demonstrate impacts of shale gas activities. Isotopic analyses should be included in the routine monitoring plan. The use of both residential and observation wells proved to be enlightening. While monitoring wells drilled for the project can provide a variety of valuable information, caution should be taken when interpreting alkane concentration results, as some of these wells showed either increasing or decreasing values in the first few months, with implications for the determination of gas origin.
Résumé(Résumé en langage clair et simple, non publié)
Les concentrations de méthane dissous dans l'eau souterraine ne varient pas seulement spatialement, mais aussi dans le temps et en fonction de la méthode utilisée. Cependant, très peu d'études ont suivi dans le temps ces variations. Un projet a été réalisé dans le sud du Québec (St-Édouard) pour étudier les impacts potentiels des activités liées au développement de gaz de shale sur les aquifères et ces variations ont aussi été étudiées. Cette étude confirme que le fait de réaliser une seule campagne d'échantillonnage basée uniquement sur les concentrations de méthane ne fournit pas un portrait précis de l'environnement avant exploitation, qui pourrait servir à démontrer les impacts des activités liées au développement des gaz de shale. Les analyses isotopiques devraient être inclues dans le suivi et la même méthode d'échantillonnage devrait systématiquement être utilisée.