--> Distribution of Sedimentary Heterogeneities in Shale Plays: Insight From Sequence Stratigraphy, Multi-Proxies Analysis and Stratigraphic Modeling of the Montney and Doig Formations (Trias, Alberta-British Columbia, Canada)

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Distribution of Sedimentary Heterogeneities in Shale Plays: Insight From Sequence Stratigraphy, Multi-Proxies Analysis and Stratigraphic Modeling of the Montney and Doig Formations (Trias, Alberta-British Columbia, Canada)

Abstract

In self-sourced reservoirs, the occurrence of hydrocarbons is linked with in-situ organic content and thermal maturity, while the effective extraction of this resource depends on the brittleness of the reservoir which is mainly controlled by the mineralogy and the rock fabric. The aim of this study is to improve the understanding of sedimentary heterogeneities in shale plays, based on outcrop and well data from the Triassic Montney and Doig Formation (Fms). Our workflow comprises 3 stages: (1) Well correlations, based on sequence stratigraphy, provide an understanding of the 3D stratigraphic architecture of the basin. (2) Integration of Rock-Eval VI, ICP-MS/AES and QEMSCAN analysis of cores, cuttings and outcrop samples distributed along a basin-wide cross-section helps to identify the factors controlling the organic content heterogeneities (dilution, destruction, production) as well as their associated mineralogy. (3) A process-based forward modeling of the stratigraphic evolution of the basin with Dionisos-Flow. It provides a quantification of the controlling factors as well as 3-D distribution of reservoir heterogeneities at basin-scale. Depositional setting of the Montney and Doig Fms ranges from tidal to offshore environments, with an episode of turbiditic and contouritic sedimentation. Our analysis of the stratigraphic architecture of the Montney and Doig Fms highlighted four third-order sequences. The “Doig Phosphate” forms a major heterogeneity at the base of the fourth sequence, with present-day TOC values up to 10 wt% and immature TOC estimations up to 14 wt%. QEMSCAN analysis showed that the Montney and Doig Fms are mainly composed of quartz, feldspars, carbonates and clay minerals (less than 25%). This low clay content differentiates them from the Utica and Eagle Ford shale plays. The integration of the geochemical analysis in the stratigraphic framework showed that the organic content in the Montney and Doig Fms is controlled by different combinations of: organic production, dilution and destruction, depending on the location along the depositional profile and on the systems tracts. Lastly the stratigraphic modeling provided the opportunity to quantify the complex distribution of organic content heterogeneities and their associated mineralogy. The dynamic of dilution, destruction and production processes can thus be spatially and temporally quantified and correlated with the stratigraphic architecture and the dynamic of the basin.