Abstract

Two-dimensional petroleum systems models (PSMs) are calculated for a cross-section through Hecate Strait in order to estimate the timing of hydrocarbon generation, expulsion and migration in the Queen Charlotte Basin, offshore BC, Canada. Our PSMs account for dominant kerogen types in the potential source rocks, and predict timing of generation, expulsion, and migration patterns of petroleum. The PSMs highlight the importance of fault zones for migration and potential loss of petroleum through the seafloor.

Rich marine Jurassic source rocks (Ghost Creek Formation, Sandilands Formation) are assumed to underlie Hecate Strait. We predict these source rocks to be overmature with more than 80% kerogen transformation into oil and gas (>27 kg petroleum/t rock), even if significant heating was only restricted to Tertiary rifting. Our PSMs predict that most of the petroleum has been expelled from the source beds, with some potential seepage loss to the surface.

Cretaceous source rocks are thicker and more extensive with less structural deformation on Haida Gwaii. They have variable, but generally low total organic carbon (TOC) content. If time equivalent sediments exist under Hecate Strait, they are likely to be terrestrial, Type III kerogen. Basin-wide, these source rocks are not considered to be highly productive, and only where they are buried >4.1 km (an area of approximately 2700 km2) do we calculate a transformation ratio >50%. Only a minor amount of Cretaceous derived petroleum is anticipated to have migrated and accumulated in the overlying Skonun Formation sediments, which comprise the most extensive and suitable reservoir facies.

No significant accumulations of hydrocarbon are expected from the terrestrial, Mio-Pliocene Skonun Formation source rocks. The area of the basin, where the anticipated transformation ratio exceeds 50% is less than approximately 1400 km2.

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