Abstracts

160 - A study of potential links between the Utica Shale and
shallow aquifers in St-Édouard, southern Québec, Canada
Rivard, C., Bordeleau, G., Lavoie, D., Ladevèze, P., Duchesne, M., Pinet, N., &
Ahad, J.
Geological Survey of Canada, Québec City, Québec, Canada
Lefebvre, R. & Aznar, J.-C.
Institut national de la Recherche scientifique – Centre Eau Terre Environnement (INRS-
ETE), Québec City, Québec, Canada
Pugin, A. & Crow, H.
Geological Survey of Canada, Ottawa, Ontario, Canada
Séjourné, S.
Consulting geologist, Montréal, Québec, Canada
Labrie, D.
CanmetMINING, Ottawa, Ontario, Canada
Potential links between a deep gas shale formation and shallow aquifers are being investigated
in southern Quebec (Canada), near a shale gas well drilled and fracked in 2009-2010.
A large set of data has been collected to detect potential natural fluid migration pathways.
Acquired data include hydrogeological, geophysical, geochemical, as well as geomechanical
data. Hydrogeological work involved drilling, permeability tests and structural surveys
of outcrops. Geophysical surveys comprised shallow high-resolution seismic, borehole logging
in the newly drilled shallow wells, as well as airborne Transient-Electro-Magnetic and
magnetic surveys. Groundwater from 44 wells was sampled and analyzed for a wide range
of compounds, and 6 of these wells were chosen for continued monitoring of dissolved
alkane concentration and isotopes (every 3 months). Soil and core samples were also collected
to determine their hydrocarbon content. Geomechanical properties of deep shale
formations were studied using both acoustic geophysical logs and core samples.
Geochemical data show that methane is present throughout the study area, but in highly
variable concentrations (from nearly 0 to 40 mg/L), while ethane and propane are only
found in a few wells. Preliminary results indicate that alkane concentrations are strongly
correlated to the water type, well depth and groundwater age. They also show that all
samples would contain bacteriogenic methane, and from 20 to 40% would also have a thermogenic
component. Additional analyses on groundwater and core samples are ongoing
to better identify the methane source. The geophysical interpretation, including deep and
shallow data, suggests that possible pathways could be present. However, hydraulic tests
have not indicated different permeabilities close to known faults. Permeabilities in the
shallow and naturally fractured shale rock aquifers vary from moderate where sandstone
beds occur (10 -6 – 10 -7 m/s) to low when mostly black shale is present (10 -9 -10 -8 m/s).
Borehole logging showed that most of the permeable fractures occur in the upper 40 m
and that permeability usually rapidly decreases with depth. Brackish water in one well
was encountered at about 140 m deep, confirming that active groundwater flow is very
shallow. Geomechanical data further indicate that the caprock geological units above the
gas shale act as a good protection against potential contamination from deep fluids. This
study integrates data from multiple sources in order to acquire the necessary knowledge to
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