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TitleNumerical modeling of hydrocarbon generation in the Douglas Formation of the Athabasca Basin (Canada) and implications for unconformity-related uranium mineralization
AuthorChi, G; Li, Z; Bethune, K
SourceJournal of Geochemical Exploration vol. 144, pt. A, 2014 p. 37-48, https://doi.org/10.1016/j.gexplo.2013.10.015
Year2014
Alt SeriesEarth Sciences Sector, Contribution Series 20130328
PublisherElsevier BV
Documentserial
Lang.English
Mediaon-line; digital
File formatpdf; html
ProvinceSaskatchewan
NTS64E; 64L; 64M; 74E; 74F; 74G; 74H; 74I; 74J; 74K; 74L; 74M; 74N; 74O; 74P
Areanorthern Saskatchewan
Lat/Long WENS-112.0000 -102.0000 60.0000 57.0000
Subjectsgeochemistry; fossil fuels; economic geology; models; modelling; uranium; mineralization; mineral occurrences; mineral deposits; hydrocarbons; hydrocarbon geochemistry; hydrocarbon potential; hydrocarbon generation; Athabasca Basin; Douglas Formation; Precambrian; Proterozoic
Illustrationslocation maps; cross-sections; plots
ProgramUranium Ore Systems, Targeted Geoscience Initiative (TGI-4)
AbstractThe Proterozoic Athabasca Basin in Canada is known for its world-class, high-grade uranium deposits developed near the unconformity between the basin and the basement. The Douglas Formation in the upper part of the preserved strata in the basin contains total organic carbon (TOC) of up to 3.56 wt.%. Previous studies of organic matter maturation and hydrocarbon inclusions indicate that oil and gas have been generated from this formation, and that some hydrocarbons found in the unconformity-related uranium deposits were derived from the Douglas Formation. This study aims to evaluate how the oil and gas generation processes may have affected the fluid overpressure development in the basin, and whether or not the hydrocarbons generated in the Douglas Formation could migrate downward to stratigraphically lower intervals and eventually to the sites of mineralization near the unconformities. We carried out a series of numerical experiments to examine fluid overpressures, flow directions, temperatures, and oil and gas generation processes using a two-dimensional conceptual model derived from a geologic cross-section from the basin center to the eastern margin. An additional 5 km strata were added to current basin stratigraphy to account for observed paleogeothermal data. Variation studies were undertaken to account for uncertainties in the lithologies of the eroded strata, and the wide ranges of possible permeabilities of different lithologies and kinetic parameters of oil and gas generation. It is found that, if moderate permeabilities are used in the modeling for each lithology (known as the base model), oil and gas generation processes contribute little to the development of fluid overpressure, and fluid pressure in the basin is close to hydrostatic regardless of whether or not hydrocarbon generation in the Douglas Formation is included in the modeling. However, if permeabilities are assigned values one order of magnitude lower than in the base model, significant fluid overpressures are developed in the eroded strata in the upper part of the model. In the base model, oil generated in the Douglas Formation may migrate downward, driven by an overpressure zone situated above the Douglas Formation, but gas migrates upward. In the low-permeability model, however, the overpressures developed above the Douglas Formation are so high that both oil and gas generated in the Douglas Formation migrate downward. The numerical modeling results thus indicate that it is hydrodynamically possible for oil and gas generated in the Douglas Formation to migrate to the base of the basin and reach the sites of the unconformity-related uranium deposits.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. The Proterozoic Athabasca basin in Canada is known for its world-class, high-grade uranium deposits developed near the unconformity between the basin and the basement. Previous studies have proposed that oil and gas were generated from upper strata in the basin and that some of these hydrocarbons played a role in formation of the unconformity-related uranium deposits. The numerical modeling generated in this study indicate that it is hydrodynamically possible for oil and gas generated in the upper strata to migrate to the base of the basin and reach the sites of the unconformity-related uranium deposits.
GEOSCAN ID293331