Sequence stratigraphic architecture of the Lower Triassic Montney Formation, northeastern British Columbia, Canada

The Lower Triassic Montney Formation in western Canada is the third largest unconventional natural gas deposit globally. The project area lies at the basinward limit of subsurface deposition and exhibits a wide degree of heterogeneity. Four stratigraphic se-quences bounded by either coplanar sequence boundary-flooding surfaces or their correlative conformities are recognized in the Montney and overlying Sunset Prairie Formation and are matched to global Triassic substages. These sequences and substages include sequence 1 (Griesbachian-Dienerian, lower Montney), sequence 2 (Smithian, middle Montney), sequence 3 (Spathian, upper Montney), and sequence 4 (Anisian, Sunset Prairie). Sequence 1 consists of a retrogradational to aggradational set of distal ramp parasequences. Sequence 2 is composed of prograding mixed siliciclastic-carbonate ramp parasequences. Sequence 3 is made up of two distinct successions. The lower interval reflects deposition in offshore environments during onlap, whereas the overlying interval is an offlapping set of shoreface parasequences. Sequence 4 was deposited within an offshore to lower shoreface setting.With petrophysical logs, subsurface core, and biostratigraphic data, higher-resolution parasequences may be identified within each of these four sequences. Sequence 1 can be further subdi-vided into three parasequence sets (LmA-LmC) and one separate parasequence (LmD), sequence 2 into four parasequence sets (MmA-MmD) and one separate parasequence (MmE), sequence 3 into five parasequence sets (Um1-UmC), and sequence 4 into one large parasequence unit (Am1). Understanding these different parasequences and their spatial distribution is critical when consid-ering variations in static reservoir properties and their relation to dynamic well performance.

Automated summary

The Lower Triassic Montney Formation in western Canada is the third largest unconventional natural gas deposit globally. It exhibits a wide degree of heterogeneity and consists of four stratigraphic sequences matched to global Triassic substages. Understanding these sequences and their spatial distribution is critical for considering variations in static reservoir properties and their relation to dynamic well performance.