Multiscale Elucidation of kerogen heterogeneity in Lucaogou Formation based on experiment and simulation: Structural Determinants of reactivity and stability for shale oil conversion

Abstract

Despite breakthroughs in continental shale oil exploitation within the Lucaogou Formation of the Junggar Basin in Xinjiang, China, divergent structural and molecular characteristics between the kerogens of the upper and lower sub-members remain poorly understood. This study bridged this knowledge gap by integrating multiscale experimental characterizations—solid-state ¹³C NMR, XPS, Py-GC/MS, FT-IR, and XRD—with computational simulations and revealed the influence of kerogen structure on shale oil conversion. Variations in aliphatic carbon distributions and degree of aromatic polymerization within Lucaogou kerogens directly account for differences in produced shale oil properties. Specifically, upper-section kerogen contains predominantly linear methylene chains, while lower-section kerogen features highly branched aliphatic chains and abundant aliphatic rings. Elevated aromatic substitution in upper kerogen promotes hydrocarbon generation through dealkylation, while higher condensation in lower kerogen suppresses thermal cracking. Nitrogen and sulfur species in kerogen primarily exist as aromatic heterocycles, which may inhibit free radical reactions at lower temperatures. Quantum chemical analysis was performed on molecular models constructed from experimental data. This analysis shows that oxygen atoms bonded to aromatic rings create potential electrophilic substitution sites on specific aromatic carbon atoms. Furthermore, alicyclic rings demonstrate higher susceptibility to ring-opening reactions. This is attributed to their lower bond dissociation energy compared to other CC bonds structures. The HOMO-LUMO (highest occupied molecular orbital/lowest unoccupied molecular orbital) distribution enhances site-specific reactivity, governed by substituent electronic effects and conjugation. These findings elucidate critical structure–function relationships, offering theoretical guidance for Lucaogou shale oil exploration and conversion processes.