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TitleMethane variations in groundwater
AuthorRivard, C; Bordeleau, G; Lavoie, D; Lefebvre, R; Malet, X; Ahad, J
SourceAmerican Association of Petroleum Geologists, Annual Meeting Abstracts .
Alt SeriesEarth Sciences Sector, Contribution Series 20160261
PublisherAmerican Association of Petroleum Geologists (AAPG)
MeetingAmerican Association of Petroleum Geologists (AAPG) Annual Convention & Exhibition 2017 (ACE2017); Houston, TX; US; April 2-5, 2017
Documentserial
Lang.English
Mediapaper
ProvinceQuebec
Subjectsfossil fuels; hydrogeology; sedimentology; methane; gas; groundwater; hydrocarbons; shales; environmental impacts
ProgramShale Gas - seismicity, Environmental Geoscience
AbstractMethane 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.
Summary(Plain Language Summary, not published)
Methane concentrations in groundwater not only vary spatially for a given region, they also vary both over time and with the sampling technique. However, very few studies have monitored these variations. A project was conducted in southern Quebec (St-Édouard) to study potential impacts of hydrocarbon development on groundwater and these issues were also addressed. 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 and the same sampling method should consistently be used.
GEOSCAN ID299418