A study of groundwater quality from domestic wells in the Sussex and Elgin regions, New Brunswick: with comparison to deep formation water and gas from the McCully gas field
Authors: Al T A , Leblanc J , Phillips S 
Published: September 2013

The exploration for shale gas in Canada has led to the identification of a huge volume of in-place and marketable natural gas with the potential of supplying clean burning fuel for many decades. However, some controversies exist on the technique used to unlock
these new riches; that is hydraulic fracturing from high-pressure injection of slickwater, a mixture of water, chemicals and proppants (sand) in order to create and keep open small fractures in the target shale.
The Carboniferous Frederick Brook shale and the overlying Hiram Brook sandstone in southern New Brunswick are identified as promising sources for shale gas. Preliminary evaluation of in-place resources by one operator in the Moncton sub-basin suggests 67 Tcf of natural gas in their acreage. At the
McCully gas field, there is production from one vertical well in the Frederick Brook shale but most of the production is from tight sandstone of the Hiram Brook Member. Initial exploration specific to shale gas has led to high expectations but inconclusive results. In the same period, societal
concerns about the risk of groundwater contamination from shale gas exploration activities have increased significantly in New Brunswick. The Geological Survey of Canada, in collaboration with eastern Canada provincial stakeholders has initiated a four-year research project (2011-2015) designed to
evaluate the potential of natural connectivity between the deep-seated shales and the shallow groundwater.
In 2012-2013, the Department of Earth Sciences at the University of New Brunswick carried out a sampling program of 26 water wells from the area around the McCully gas field near Sussex; the operator of the McCully gas field provided gas and brine samples for chemical and isotopic comparison. This
gas field has experienced multiple hydraulic fracturing events in vertical wells for the development of the tight sandstone gas reservoir from 2000 to 2008.
The research program consisted of field measurements (pH, redox and alkalinity) as well as groundwater sampling for isotope analyses (18O and 2H) and inorganic chemistry, measurements of dissolved hydrocarbons (methane, ethane and propane) and isotope analyses (13C and 2H) of dissolved methane.
Methane from the gas field was isotopically characterized as well as the inorganic chemistry of the brine.
The McCully brine has concentrations of Na, Cl and Br that are hundreds of times higher than that of shallow groundwater. Concentrations of K, Ca, Mg and SO4 are also higher than those of shallow groundwater; from its chemistry, the brine is likely derived from seawater and comparison with shallow
groundwater does not indicate mixing.
Gas produced at McCully is methane (91 -- 94%) with ethane (2 -- 6%) and propane (0.1 -- 1%). Isotopic analyses of the methane suggest a thermogenic origin. No ethane or propane was measured in the groundwater and methane was detected in 3 domestic wells. Concentrations are very low
(0.01, 0.11 and 1.17 mg/L); the 3 samples are outside the McCully gas field area. Two of these samples had enough methane for isotopic analyses, one suggestive of a thermogenic origin and the other is enriched in 2H that could be related to oxidation of methane.