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TitleOrigin of sulfate-rich fluids in the Early Triassic Montney Formation, Western Canadian Sedimentary Basin
AuthorLiseroudi, M H; Ardakani, O HORCID logo; Sanei, HORCID logo; Pedersen, P K; Stern, R A; Wood, J M
SourceMarine and Petroleum Geology vol. 114, 104236, 2020 p. 1-17,
Alt SeriesNatural Resources Canada, Contribution Series 20180141
Mediapaper; on-line; digital
File formatpdf; html; xml
ProvinceAlberta; British Columbia
NTS83L/09; 83L/10; 83L/11; 83L/12; 83L/13; 83L/14; 83L/15; 83L/16; 83M; 84D; 84E/03; 84E/04; 93I/09; 93I/16; 93P/01; 93P/02; 93P/06; 93P/07; 93P/08; 93P/09; 93P/10; 93P/11; 93P/13; 93P/14; 93P/15; 93P/16; 94A; 94B/01; 94B/08; 94B/09; 94B/16; 94G/01; 94H/01; 94H/02; 94H/03; 94H/04
AreaDawson Creek
Lat/Long WENS-122.3333 -118.0000 57.2500 54.6667
Subjectsfossil fuels; sedimentology; geochemistry; Science and Technology; Nature and Environment; Lower Triassic; diagenesis; formation fluids; fluid dynamics; provenance; sulphates; anhydrite; barite; pyrite; reservoir rocks; hydrogen sulphide; sour gas; paragenesis; cementation; fractures; stable isotope studies; radioisotopes; sulphur; oxygen; strontium strontium ratios; bedrock geology; basement geology; sedimentary rocks; siltstones; shales; evaporites; mass spectrometer analysis; core samples; petrographic analyses; hydrothermal systems; structural controls; Montney Formation; Western Canadian Sedimentary Basin; Phanerozoic; Mesozoic; Triassic; Paleozoic; Devonian
Illustrationslocation maps; geoscientific sketch maps; stratigraphic columns; cross-sections; tables; photomicrographs; photographs; charts; plots; profiles; time series
ProgramGeoscience for New Energy Supply (GNES) Shale Reservoir Characterization
Released2020 01 11
AbstractThis study investigates diagenetic and geochemical processes that control regional distribution and formation of sulfate minerals (i.e., anhydrite and barite) in the Early Triassic Montney Formation in the Western Canadian Sedimentary Basin. The generation of H2S in hydrocarbon reservoirs is often associated with the dissolution of sulfate minerals, as a major source of sulfate required for sulfate-reducing reactions. The formation of pervasive late diagenetic anhydrite and barite in the high H2S zone of the Montney Formation is therefore contrary to the normal paragenetic sequence of sour gas reservoirs.
Petrographic observations revealed early and late anhydrite and barite cement. The early fine-crystalline anhydrite cement is dominant in northeastern British Columbia (low H2S zone), while the late-stage coarse-crystalline cement and fracture/vug-filling anhydrite are dominant in Alberta (high H2S zone). The bulk isotopic values (delta-34S: +2.9 to +24.7 per mille V-CDT, delta-18O: -11.2 to +15.7 per mille V-SMOW) suggest that sulfate-rich fluids originated mainly from modified Triassic connate water was the origin of early anhydrite. In contrast, the SIMS isotopic values of late anhydrite (delta-34S: +18.5 to +37 per mille V-CDT, delta-18O: +12 to +22 per mille V-SMOW) and barite cement (delta-34S: +23.3 to +39 per mille V-CDT, delta-18O: +13.2 to +18.7 per mille V-SMOW) as well as fracture/vug-filling anhydrite (delta-34S: +23.5 to +24.7 per mille V-CDT, delta-18O: +13.3 to +14.7 per mille V-SMOW) from Alberta represents a mixed isotopic signature of Triassic connate water and contribution of dissolved sulfate-rich fluids derived from dissolution of Devonian evaporites.
The 87Sr/86Sr isotope ratios of the fracture/vug-filling anhydrite (0.7092-0.7102) are highly radiogenic suggesting extensive water/rock interactions between sulfate-rich fluids and siliciclastic and basement rocks. The similar isotopic composition of the late anhydrite/barite and fracture/vug-filling anhydrite in western Alberta with Devonian evaporites isotopic signature, and the highly radiogenic 87Sr/86Sr ratio further supports sulfate-bearing fluids were mainly originated from underlying Devonian evaporites and migrated upwards through deep-seated faults/fractures to the Montney Formation.
Summary(Plain Language Summary, not published)
High concentrations of H2S in gas-producing wells from the Montney Formation in western Alberta have raised concern over the economic impact of extraction and processing of the natural gas and its adverse environmental impacts. This study investigates diagenetic and geochemical processes that control H2S generation and its regional variation in the tight natural gas play of the Lower Triassic Montney siltstone in the Western Canadian Sedimentary Basin (WCSB).

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