Relationship between hydrogen sulphide (H2S) distribution and regional burial/uplift history in the Lower Triassic Montney Formation, northeastern British Columbia, Canada
Date
2022-03-18
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Abstract
Understanding a basin’s thermal history is essential when examining past and current fluid distributions. Knowledge of the origin of non-hydrocarbon gases, including hydrogen sulphide (H2S), aids in understanding the complex organic-inorganic interactions that control basin evolution. This study provides a preliminary workflow to estimate the regional burial and uplift/erosion history of the Lower Triassic Montney Formation using a Lower Cretaceous Mannville Group vitrinite reflectance dataset. The calculated maximum burial is a first-order thermal maturity proxy. Results show variations in regional Montney burial and uplift. Specifically, increased uplift/erosion in the central area of the Montney and relatively less uplift and erosion toward the southern extent of the play. To better understand controls on the highly variable H2S distribution, identified facies are constrained within a detailed stratigraphic framework in northeastern British Columbia, highlighting the vertical and lateral facies heterogeneity (Township 79-81 and Ranges 18-14). Additionally, local structural lineaments may have influenced fluid migration. Sulphate-rich fluids migrating through fractures may preferentially enter laterally permeable units. Due to regional burial history variations, fracture cementation is likely non-uniform, meaning not all fractures are fluid conduits. Depending on the location within the basin, a once permeable unit may now have diagenetic cementation, creating lateral permeability variations for sulphate-rich fluid migration. The current Montney Formation H2S content predominantly results from in situ thermochemical sulphate reduction (TSR). The regional burial variations result in thermal differences, implying that TSR should also be non-uniform across the Montney. Upper Montney H2S concentration increases eastward within the study area, likely due to up-dip migration through permeable coarser-grained siltstones and trapping due to stratigraphic pinch out. Additionally, the elevated H2S is likely influenced by extraformational factors, including eastward thinning of the Middle Triassic succession, bringing the evaporite-rich Charlie Lake Formation into proximity with the Montney. Moreover, the Sunset Prairie Formation directly overlies the Montney and has an erosional edge that correlates to elevated Upper Montney H2S. Both relationships may lead to more significant amounts of sulphate minerals in the east supplying the sulphate required to generate H2S via TSR.
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Keywords
H2S, Montney, Hydrogen Sulphide, Burial, Uplift, Stratigraphy, Facies
Citation
Mackie, S. J. (2022). Relationship between hydrogen sulphide (H2S) distribution and regional burial/uplift history in the Lower Triassic Montney Formation, northeastern British Columbia, Canada (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.