Contribution of Montney Sourced Hydrocarbons to the Doig and Montney Petroleum System in Western Canada Sedimentary Basin

Abstract

Previously acquired biomarker analyses of oil samples and Rock-Eval analyses of cores and cutting samples have been integrated with new Rock-Eval analyses to determine the source rock potential of Montney Formation. Furthermore, the geochemical signature of Montney organic matter is used to evaluate the relative contributions of Montney-sourced hydrocarbons and Doig-sourced hydrocarbons to the Triassic petroleum system. A source rock evaluation indicates that the Montney Formation contains intervals of good hydrocarbon source rock that generated large volumes of hydrocarbons. An empirical relationship between TOC and gamma ray (GR) values is established to determine the TOC values in Montney Formation and to quantify the thickness of Montney source rock. There are three end members of oil families (Family A, Family B and Family C) with distinct geochemical signatures in the Triassic oil accumulations of Western Canada Sedimentary Basin (WCSB). Family A oils are characterized by low ratios of diasterane/regular sterane and Ts/Tm, high ratios of C24Tetracyclic terpane over C26 tricyclic terpanes and C29/C30 hopanes, a high C35 homohopane index and high sulfur contents. Family B oils are characterized by a moderate C24 tetracyclic terpane over C26 tricyclic terpane ratio, high abundances of hopanes, a low C35 homohopane index, a high diasterane/regular sterane ratio and relatively low C28 regular sterane. Family C oils show abundant extended tricyclic terpances and almost no hopanes. Source rock characteristics of Montney Formation, Doig Formation and Jurassic Gordondale Member are analysed and applied for oil-to-source rock correlations. Studies show that Family A oils are linked to a calcareous source rock and interpreted to be originated from Jurassic Gordondale Member. Family B oils are correlated with Doig source rock extracts and believed to be derived from Doig phosphate. Family C oils are interpreted to be originated from the Montney Formation. A volumetric method (Schmoker’s formula) is applied to calculate the in-place resources generated from Montney and Doig source rocks based on thermal degradation of different type of kerogens. It is inferred that the contribution of Montney sourced hydrocarbons is approximately 3.7 times that of the contribution of Doig sourced hydrocarbons in the Doig and Montney petroleum system.