Abstract

The origin, timing, and evolution of hydrocarbons in the early Triassic Montney Formation siltstone has long been debated and is poorly understood. A proper understanding of the timing and processes involved in hydrocarbon emplacement forms an important part of in-situ fluid characterization. Presented here is a case study from northeastern British Columbia. This study integrates basin modeling, carbon isotope geochemistry, fluid inclusion microthermometry, organic and inorganic petrography, sedimentology, and stratigraphy to reconstruct the burial history and relative timing of geological events and mechanisms involved in developing the present-day Montney hydrocarbon system in the Blueberry sub-play.

Petrography from whole core indicates that the organic material present is largely pyrobitumen. The lack of primary kerogen suggests that the original oil charge must have migrated into place prior to increasing thermal maturity and conversion to pyrobitumen at maximum burial. In addition, patterns in stable carbon isotope curves from extracted core fluids show a stratified oil column, indicating a lack of vertical migration that would have homogenized the hydrocarbons. Thin section petrography and facies analysis show a laminated fabric with strong permeability anisotropy suggesting preferential migration along bed-parallel permeability pathways, which would have prevented significant vertical mixing. Any interpretations about the origins of the Montney Formation hydrocarbons in this study area must satisfy these observations. Given the data available, the most likely interpretation is a bed-parallel eastern migration from a downdip source.

Collective understanding of these datasets helps illustrate the processes involved in the evolution of the hydrocarbon system present in the Montney Formation. Enhanced understanding of the Montney hydrocarbon migration history and reservoir evolution is important for understanding the lateral and vertical variations in the producing gas-condensate-ratios across the Montney formation fairway.