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TitleDeep groundwater circulation and associated methane leakage in the Northern Canadian Rocky Mountains
AuthorGrasby, S E; Ferguson, G; Brady, A; Sharp, C; Dunfield, P; McMechan, M
SourceApplied Geochemistry; Chemical Geology vol. 68, 2016 p. 10-18,
Alt SeriesEarth Sciences Sector, Contribution Series 20150144
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia; Alberta
NTS84L/03; 84L/04; 84L/05; 84L/06; 84L/11; 84L/12; 84L/13; 84L/14; 84M/03; 84M/04; 84M/05; 84M/06; 84M/11; 84M/12; 84M/13; 84M/14; 85D/03; 85D/04; 85D/05; 85D/06; 94I; 94J; 94K/01; 94K/02; 94K/07; 94K/08; 94K/09; 94K/10; 94K/15; 94K/16; 94N/01; 94N/02; 94N/07; 94N/08; 94N/09; 94N/10; 94N/15; 94N/16; 94O; 94P; 95A/01; 95A/02; 95A/03; 95A/04; 95A/05; 95A/06; 95A/07; 95A/08; 95B/01; 95B/02; 95B/03; 95B/04; 95B/05; 95B/06; 95B/07; 95B/08; 95C/01; 95C/02; 95C/07; 95C/08
AreaLiard Line; Larsen Fault
Lat/Long WENS-125.0000 -119.0000 60.5000 58.0000
Subjectsenvironmental geology; fossil fuels; hydrogeology; groundwater; groundwater geochemistry; springs; oil shales; shales; geothermal temperatures; geothermal fluids geochemistry; hydrocarbon gases; gas seeps; hydraulic fracturing; fracturing; environmental impacts; health hazards; hydrocarbon gases; hydrocarbon migration; hydrothermal systems; reservoir fluids; Ordovician; Devonian
Illustrationslocation maps; thermal maps; isotope graphs; ternary diagrams; tables; cross-sections, structural; cross-sections, stratigraphic
ProgramShale Reservoir Characterization, Geoscience for New Energy Supply (GNES)
AbstractConcern over potential impact of shale gas development on shallow groundwater systems requires greater understanding of crustal scale fluid movement. We examined natural deeply circulating groundwater systems in northeastern British Columbia adjacent to a region of shale gas development, in order to elucidate origin of waters, depths of circulation, and controls on fluid flow. These systems are expressed as thermal springs that occur in the deformed sedimentary rocks of the Liard Basin. Stable isotope data from these springs show that they originate as meteoric water. Although there are no thermal anomalies in the region, outlet temperatures range from 30 to 56 \'01C, reflecting depth of circulation. Based on aqueous geothermometry and geothermal gradients, circulation depths up to 3.8 km are estimated, demonstrating connection of deep groundwater systems to the surface. Springs are also characterised by leakage of thermogenic gas from deep strata that is partly attenuated by methanotrophic microbial communities in the spring waters. Springs are restricted to anomalous structural features, cross cutting faults, and crests of fault-cored anticlines. On a regional scale they are aligned with the major tectonic features of the Liard Line and Larsen Fault. This suggests that while connection of surface to deep reservoirs is possible, it is rare and restricted to highly deformed geologic units that produce permeable pathways from depth through otherwise thick intervening shale units. Results allow a better understanding of potential for communication between deep shale gas units and shallow aquifer systems.
Summary(Plain Language Summary, not published)
Controls on natural occurrence of deep crustal circulation systems and methane leakage to surface were examined to elucidate controls on connection of deep fluids to shallow groundwater systems in regions adjacent to shale gas development. In the study areas the rocks are highly deformed by mountain building processes and are equivalent to those in the undeformed sedimentary basin to the east that host the Horn River shale gas play. Results show that natural groundwater systems circulate to depths of 2.9 km and allow leakage of thermogenic gas to surface. However, these natural systems are rare and restricted only to areas of highly deformed rock. This suggests that while connection of deep fluid systems to surface are possible, they are uncommon even where rock are highly deformed.