Origin of bitumen fractions in the Jurassic-early Cretaceous Vaca Muerta Formation in Argentina: insights from organic petrography and geochemical techniques

This paper investigates chemical functional groups of the two extracted bitumen fractions in shales of the Jurassic to early Cretaceous Vaca Muerta Formation of the Neuquen Basin in Argentina, South America. The results indicate that Bitumen I is strongly aliphatic and appears to be genetically related to fluorescent amorphous organic matter. In contrast, Bitumen II consists of highly condensed, aromatic hydrocarbons, and has some correspondence to nonfluorescent amorphous organic material. Comparison of Rock-Eval VI pyrolysis data (S1 and S2) with the bitumen yields suggests that Bitumen I relates to S1 but also to S2. In addition, Bitumen I has a positive correlation with light liquid hydrocarbons (C-5-C-29), but also partially with heavier hydrocarbons (above C-30). This suggests that Bitumen I corresponds to the majority of lighter hydrocarbons up to C-29 and some portion to heavier hydrocarbons. These results have implications for the assessment of the mobility of generated hydrocarbons and their availability for production.