Stratigraphy, facies heterogeneities, and structure in the Montney Formation of northeastern British Columbia: relation to H2S distribution

In the last decade, the Lower Triassic Montney Formation of the Western Canada Sedimentary Basin (WCSB) has undergone significant development, providing a rich dataset to study structural, stratigraphic, and facies control on the variations in hydrogen sulphide(H2S) gas content. Splitting the siltstone dominated Montney into the three regional members (i.e., Lower Montney, Middle Montney, and Upper Montney) allows for detailed analysis on the enrichment of H2S within a local-scale study area in northeastern British Columbia (BC). Within this study area,Upper Montney H2S content increases within individual parasequences both up-dip and towards the east. In addition to potential up-dip migration, there may be greater sulphur-bearing components in the east, allowing for the sulphate reduction required to generate H2S. The overlying Middle Triassicthins eastward, providing proximity to the overlying anhydrite-rich beds of the Upper Triassic Charlie Lake Formation. Further, the overlying Middle Triassic Sunset Prairie Formation has an erosional edge that corresponds with eastern elevated H2S concentrations within the Upper Montney unit. Mappedstructures are syn-depositional to the Middle Triassic, potentially providing conduits for early sulphate-rich fluid migration.In the Middle and Lower Montney, elevated H2S generally occurs with proximity to the top of the Permian Belloy Formation. Within this study area, limited Lower Montney data is available and thus needs to be further corroborated with regional data. Both the Middle and Lower Montney display elevatedH2S in trends that generally align with mapped faults. The faults may have acted as conduits for sulphate-rich fluids to migrate during early burial then migrate laterally through facies that may have been permeable during early burial, such as the carbonate-rich facies at the boundary between theMiddle and Lower Montney. Further core and isotope analyses are required to fully understand this relationship.