|Titre||The diagenetic continuum of hopanoid hydrocarbon transformation from early diagenesis into the oil window|
|Auteur||Synnott, D P; Schwark, L; Dewing, K; Percy, E L; Pedersen, P K|
|Source||Geochimica et Cosmochimica Acta vol. 308, 2021 p. 136-156, https://doi.org/10.1016/j.gca.2021.06.005|
|Séries alt.||Ressources naturelles Canada, Contribution externe 20210202|
|Document||publication en série|
|Media||papier; en ligne; numérique|
|Lat/Long OENS||-119.9164 -109.8903 56.9928 49.0378|
|Sujets||géochimie organique; combustibles fossiles; Sciences et technologie; géochimie|
|Illustrations||diagrammes; cartes de localisation; coupes transversales; représentations graphiques combinées; diagrammes|
|Programme||Les géosciences pour les nouvelles sources d'énergie Caractérisation des réservoirs de schiste|
|Diffusé||2021 06 11|
|Résumé||(disponible en anglais seulement)|
Hopanoid molecules are ubiquitous in sedimentary rocks and make up a significant proportion of sedimentary organic matter, oils, and bitumen. Due to their
relatively stable chemical structure, they are generally well preserved in the rock record, making them extremely useful as biomarkers or geomarkers. Despite extensive industry and scientific interest, the early phase of their eogenetic and early
diagenetic transformation has not been fully demonstrated or examined in a geologic setting. Most previous studies have focused on the oil window range from about 0.5-1.0 %VRo, and neglected transformations that happen at maturity levels below this.
Additionally, the geological transformation of hopanoids has been extensively applied as a geochemical indicator of thermal maturity, however the mechanisms that result in these transformations are not fully understood. A major stumbling block in the
study of hopanoid diagenesis is the availability of well constrained samples along a single stratigraphic horizon from very low maturity and through the oil window. This study utilizes a natural thermal maturity transect along a single stratigraphic
horizon which stretches from thermally immature rocks, up to the middle of the oil window. The purpose of this study is to document the progressive changes in abundance of hopanoid hydrocarbon compound classes and between individual isomers with
increasing thermal transformation. Samples for this study were taken from cores of the Upper Cretaceous Second White Specks Formation, a major source rock within the Western Canadian Sedimentary Basin, that has been extensively mapped and studied.
This sample set represents a unique opportunity to examine the changes in hopanoid class with increasing thermal maturity. 69 samples from 8 wells were examined for biomarkers. Thermal maturity was determined using HAWK programmed pyrolysis analysis
of 87 samples from 9 wells. These geochemical methods were combined with a well established stratigraphic framework to ensure that sampling methods were stratigraphically controlled. Neohopenes, hopenes, ßß-hopanes, ßa-hopanes, aß-hopanes, and
rearranged hopanes were differentiated and drastic changes in the proportions of these compound classes were observed with increasing thermal maturity. Thermally immature rocks are dominated by hopenes, neohopenes, and ßß-hopanes, whereas the middle
of the oil window is dominated by aß-hopanes and rearranged hopanes. These results allow a detailed determination of the maturity ranges that correspond to the transformation or disappearance of specific hopanoid molecule classes, for example the
loss of hopenes in the maturity range of 0.28-0.35 %VRE. Additionally, this study allows the stages of episodic or punctuated transformations of hopanoid classes to be better delineated and narrowed down to specific maturity ranges. This work
represents a novel examination of a natural thermal maturity transect and helps to consolidate our understanding of the early diagenetic transformations of hopanoid compounds.
|Sommaire||(Résumé en langage clair et simple, non publié)|
Les hopanoïdes sont un groupe commun de molécules organiques présentes dans les sédiments et les roches sédimentaires. Cet article examine
comment la structure des molécules d'hopanoïdes change avec l'augmentation de la température à mesure que les sédiments sont enfouis et transformés en roche.