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Petroleum system analysis of the Triassic Doig Formation, Western Canada Sedimentary Basin Lacerda Silva, Pablo

Abstract

The potential of the Doig Formation as an unconventional petroleum system was investigated in this study. The Triassic Doig Formation of the Western Canada Sedimentary Basin extends continuously across northeast British Columbia and central western Alberta, and it is known as a source-rock for conventional reservoirs in the basin. This investigation encompasses the mapping of source-rock properties, characterization of reservoir properties related to hydrocarbons storage capacity and producibility, lithogeochemistry and sedimentology of the basal phosphatic informal subunit, and a 3D basin model for reconstructing and determining the timing of thermogenic generation of hydrocarbons, as well as their expulsion and migration. The Doig Formation contains kerogen of Type II and III and has fair to good source rock potential. Most of the Doig subcrop area is in the early oil window, grading to overmature dry gas towards the southwest. The Doig Formation is subdivided into the basal more organic-rich Doig Phosphate Zone (DPZ), with a median of 2.7% total organic carbon (TOC), and the upper Doig, with a median of 1.3%. Porosity ranges from 0.3 to 14.6% and matrix permeability ranges from 8×10⁻⁶ to 14 mD. Matrix permeability is controlled primarily by pore throat size. Total gas in-place ranges from 6.2 to 9.7 trillion m³. Mineralogy is primarily composed of detrital quartz, diagenetic dolomite and calcite, in highly variable proportions. Clay content is low, with a median of 4.9% by weight, and apatite occurs as intraclasts and coated grains in phosphorite beds in the DPZ, which are interpreted to be a result of various phases of phosphatization, exhumation, and reburial. Mineralogy and TOC distributions reflect the fore-arc basin configuration with a southwestern paleo-high, and a connection to open marine environment to the north. Burial history reconstruction suggests subsidence rates of up to 390 m/Ma towards the Late Cretaceous, and removal of several kilometers of sediments during the Cenozoic. The Doig entered the oil window in the Albian, and generated a total mass of 69,000 million metric tons of petroleum. Approximately 50% of the gas generated may have been retained in the source-rock or migrated into tight and conventional Doig reservoirs.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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