--> Thermal Maturation Considerations and the Significance of Phytoclasts in the Upper Member of the Lodgepole Formation in the North-Western Williston Basin
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AAPG ACE 2018

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Thermal Previous HitMaturationTop Considerations and the Significance of Phytoclasts in the Upper Member of the Lodgepole Formation in the North-Western Williston Basin

Abstract

The study represents the first attempt to provide palynological data to help with the analysis of hydrocarbon source potential of the upper marker bed of the Lodgepole Formation (herein referred as the Upper Lodgepole). This study covers the southeast corner of Saskatchewan, Canada and northwest corner of North Dakota, USA. In this area, the Upper Lodgepole is a calcareous source rock that reaches a maximum thickness of roughly 30 m. X-ray diffraction calcite values range from 68-94%, total organic carbon (TOC) content from pyrolysis reaches a maximum of 9.06 wt. %, and vitrinite reflectance equivalence values from pyrolysis range from 0.76–0.87%. Based on Rock-Eval pyrolysis data, both from this study and others, it has been postulated that the Upper Lodgepole is a mature, kerogen type-II source rock that is well within the oil window. However, previous published studies have suggested that such elevated thermal maturity indicated from Rock-Eval pyrolysis is rather a result of lower hydrogen index (HI) and higher degree of oxidation. Palynological kerogen analysis of both core and cuttings unequivocally confirms the aforementioned hypothesis that organic material is indeed highly degraded. Furthermore, a detailed point count of the palynomorphs also shows the interval to contain 100% phytoclasts, a predominantly gas-prone, type-III kerogen.