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TitleGas geochemistry and the origins of H2S in the Montney Formation
DownloadDownload (whole publication)
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorLacerda Silva, P; Chalmers, G R; Bustin, A M M; Bustin, R M
SourceHydrogen sulfide (H2S) in the Montney Formation, Western Canada Sedimentary Basin (WCSB) - investigating a complex issue, workshop proceeding; by Ardakani, O HORCID logo (ed.); Pedersen, P KORCID logo (ed.); Geological Survey of Canada, Open File 8878, 2022 p. 37-44, Open Access logo Open Access
PublisherNatural Resources Canada
MeetingMontney H2S, Distribution and Origin Workshop; Calgary, AB; CA; February 9, 2022
Documentopen file
Mediadigital; on-line
RelatedThis publication is contained in Hydrogen sulfide (H2S) in the Montney Formation, Western Canada Sedimentary Basin (WCSB) - investigating a complex issue, workshop proceeding
File formatpdf
ProvinceAlberta; British Columbia
NTS83C; 83E; 83F; 83G; 83J; 83K; 83L; 83M; 83N; 83O; 84B; 84C; 84D; 84E; 84F; 84G; 84L; 93I; 93O; 93P; 94A; 94B; 94G; 94H; 94I; 94J
AreaFort St. John; Dawson Creek; Grande Prairie; Whitecourt; Peace River; Edson; Hinton
Lat/Long WENS-123.5000 -115.7500 59.0000 53.0000
Subjectsfossil fuels; geochemistry; structural geology; mineralogy; Science and Technology; Nature and Environment; Lower Triassic; sedimentary basins; petroleum resources; hydrocarbons; gas; reservoirs; hydrocarbon geochemistry; hydrogen sulphide; reservoir fluids; carbon dioxide; thermal maturation; hydrocarbon migration; hydrocarbon generation; flow structures; structural controls; isotopic studies; sulphur; oxygen isotopes; tectonic setting; sulphur geochemistry; scanning electron microscope analyses; spectroscopic analyses; x-ray diffraction analyses; anhydrite; source rocks; groundwater geochemistry; exploration guidelines; sour gas; methane; Montney Formation; Western Canada Sedimentary Basin; Montney Play; Fort St. John Graben; Charlie Lake Formation; Halfway Formation; Phanerozoic; Mesozoic; Triassic; Paleozoic; Devonian
Illustrationslocation maps; geoscientific sketch maps; plots
ProgramEnergy Geoscience Clean Energy Resources - Decreasing Environmental Risk
Released2022 03 22
AbstractThe geology of the Montney Formation and the geochemistry of its produced fluids, including nonhydrocarbon gases such as hydrogen sulfide were investigated for both Alberta and BC play areas. Key parameters for understanding a complex petroleum system like the Montney play include changes in thickness, depth of burial, mass balance calculations, timing and magnitudes of paleotemperature exposure, as well as kerogen concentration and types to determine the distribution of hydrocarbon composition, H2S concentrations and CO2 concentrations. Results show that there is first-, second- and third- order variations in the maturation patterns that impact the hydrocarbon composition. Isomer ratio calculations for butane and propane, in combination with excess methane estimation from produced fluids, are powerful tools to highlight effects of migration in the hydrocarbon distribution. The present-day distribution of hydrocarbons is a result of fluid mixing between hydrocarbons generated in-situ with shorter-chained hydrocarbons (i.e., methane) migrated from deeper, more mature areas proximal to the deformation front, along structural elements like the Fort St. John Graben, as well as through areas of lithology with higher permeability.
The BC Montney play appears to have hydrocarbon composition that reflects a larger contribution from in-situ generation, while the Montney play in Alberta has a higher proportion of its hydrocarbon volumes from migrated hydrocarbons. Hydrogen sulphide is observed to be laterally discontinuous and found in discrete zones or pockets. The locations of higher concentrations of hydrogen sulphide do not align with the sulphate-rich facies of the Charlie Lake Formation but can be seen to underlie areas of higher sulphate ion concentrations in the formation water. There is some alignment between CO2 and H2S, particularly south of Dawson Creek; however, the cross-plot of CO2 and H2S illustrates some deviation away from any correlation and there must be other processes at play (i.e., decomposition of kerogen or carbonate dissolution). The sources of sulphur in the produced H2S were investigated through isotopic analyses coupled with scanning electron microscopy, energy dispersive spectroscopy, and mineralogy by X-ray diffraction.
The Montney Formation in BC can contain small discrete amounts of sulphur in the form of anhydrite as shown by XRD and SEM-EDX results. Sulphur isotopic analyses indicate that the most likely source of sulphur is from Triassic rocks, in particular, the Charlie Lake Formation, due to its close proximity, its high concentration of anhydrite (18-42%), and the evidence that dissolved sulphate ions migrated within the groundwater in fractures and transported anhydrite into the Halfway Formation and into the Montney Formation. The isotopic signature shows the sulphur isotopic ratio of the anhydrite in the Montney Formation is in the same range as the sulphur within the H2S gas and is a lighter ratio than what is found in Devonian anhydrite and H2S gas. This integrated study contributes to a better understanding of the hydrocarbon system for enhancing the efficiency of and optimizing the planning of drilling and production operations. Operators in BC should include mapping of the Charlie Lake evaporites and structural elements, three-dimensional seismic and sulphate ion concentrations in the connate water, when planning wells, in order to reduce the risk of encountering unexpected souring.
Summary(Plain Language Summary, not published)
The origin and distribution of hydrogen sulfide (H2S) - a highly toxic and corrosive gas in conventional and unconventional resources of the Western Canada Sedimentary Basin - was the subject of many studies. The Early Triassic Montney Formation, one of the major North American unconventional gas resources, contains a significant amount of H2S in some areas. Several research teams in western Canada including the Geological Survey of Canada, the University of Calgary, and the University of British Columbia are investigating this complex issue. This workshop will provide a venue to discuss the latest scientific advancements on this topic in order to reach a better understanding of the distribution, origin, and mitigation strategies to overcome the associated economic and environmental issues. This open file report presents the proceedings of the online workshop 'Hydrogen sulfide (H2S) in the Montney Formation - investigating a complex issue' on February 9th, 2022 in Calgary Alberta, organized by the Canadian Society for Unconventional Resources (CSUR), Natural Resources Canada (NRCan), and University of Calgary.

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