Controlling factors on source rock development: implications from 3D stratigraphic modeling of Triassic deposits in the Western Canada Sedimentary Basin

Abstract

-The recent development of unconventional resources has triggered a regain of interest for source-rocks. The presence of hydrocarbons in these unconventional systems is generally associated with organic-rich sediments. This study aims at better understanding the factors controlling the accumulation of marine organic matter at basin scale, using a process-based approach. This work focuses on the Montney, Doig and Halfway Formations (Lower and Middle Triassic, Alberta and British Columbia, Canada). Recent studies show that the Triassic strata of the Western Canada sedimentary basin can be considered as a transitional period between the Paleozoic passive margin and the Jurassic foreland basin. Based on a 3D regional stratigraphic architecture and on a description of the organic rich interval distribution, a processbased numerical model (DionisosFlow and DORS) has been used to simulate the stratigraphic evolution of the Montney, Doig and Halfway Formations and reproduce the organic distribution in these formations. This modeling approach allowed us to test different scenarios of primary productivity and basin restriction and discuss the regional controls on organic matter accumulation such as dynamic of anoxia or dilution of organic matter by detrital sediments. The reconstruction of the stratigraphic architecture emphasizes a major drop of the water discharge in the basin. In the absence of any evidence supporting a link with a climate change, the drop in water discharge suggests a major modification of the drainage area of the basin, potentially associated with the early stage of the cordilleran orogeny and foreland basin evolution. The numerical simulation also shows that the primary productivity rates in the Montney and Doig Formations are characteristic of a coastal area and that a basin restriction is required to account for the level of anoxia observed in the studied Formations. Lastly, this study investigates the regional controls on organic matter accumulation and emphasizes the impact of regional paleogeographic and geodynamic evolution on the dynamic of anoxia and on the dilution.Keywords: source rocks / stratigraphic modeling / organic matter / sedimentary fluxes / primary productivity / basin anoxia Résumé -Facteurs de contrôles sur la formation des roches mères : apport d'une modélisation stratigraphique 3D des formations du Trias du bassin ouest canadien. Le développement récent des hydrocarbures non conventionnels a suscité un regain d'intérêt pour les roches mères. La présence d'hydrocarbures dans ces systèmes non conventionnels est souvent associée à des dépôts riches en matière organique primaire. Cette étude vise à mieux comprendre les facteurs contrôlant l'accumulation de la matière organique en domaine marin à grande échelle, en utilisant une approche basée sur les processus.

Organic and isotope geochemistry analysis of petroleum condensates from the unconventional portion of the Montney Formation, Western Canada

“…This charge is assumed to have been generated in-situ, within the Montney Formation, and from the kerogen contained in this rock (potentially gas-prone kerogen type III or kerogen type II-III [3,[6][7]). The carbon isotope trend (C8-C19 in Figure 11) is consistent with condensates (and oils) formed from kerogencracking, which will be referred to as normal condensates, and consists of decreasing to relatively flat trends of δ 13 C values with increasing carbon number [34][35][36][37].…”

Geochemical characteristics and depositional environments of mudstones from the Triassic Zhifang Formation in the Tongchuan Area, southern Ordos Basin, China

“…The preservation condition of organic matters is one of the main factors controlling the development of source rocks, which are mainly formed in an anoxic environment (Crombez et al, ; Demaison & Moore, ; Ding et al, ; Zou et al, ). As a result, we infer that one of key controlling factors for the poor development of source rocks in the Zhifang Formation could be the oxic–dysoxic condition.…”

Éditorial

“…The smectite profile is unusual and smectite seems to play a major role as transport agent for reactive iron which indirectly limits the preservation of the marine organic matter. Crombez et al (2017) describe numerical modeling of the sedimentary processes that lead to the preservation of organic matter in the Triassic of Western Canada. The study consists of a sensitivity analysis of various input parameters rather than a detailed reconstruction of the distribution of the organic matter.…”