Characterization of Kerogen Structures in Oil Shales

Kerogen represents the complex, insoluble organic matrix within oil shale that serves as the primary precursor to petroleum and natural gas under geological conditions. Its structural heterogeneity—ranging from aliphatic chains, aromatic clusters and heteroatom-bearing functional groups to cross-linked macromolecular networks—dictates both the quantity and quality of hydrocarbons generated during burial and thermal maturation. Characterisation of kerogen architecture combines spectroscopic, chemical and computational modalities to reveal molecular fragment distribution, aromaticity indices, pore connectivity and reactive site accessibility. Advances in solid-state NMR have quantified carbon skeletons and functional moieties, while emerging three-dimensional macromolecular models, refined by energy minimisation and reactive force field simulations, have unveiled kerogen’s spatial arrangement and pyrolytic pathways. A comprehensive understanding of kerogen structure not only underpins improved assessment of shale resources but also informs optimised extraction and upgrading strategies across diverse depositional environments.

Research from Nature Portfolio

Recent studies have advanced kerogen model structures using quantitative NMR, revealing molecular fragment evolution with thermal maturation and refining models to predict hydrocarbon generation potential more accurately. Utilising a maturity series spanning vitrinite reflectance values from 0.8 to 3.0, multi-dimensional 13C NMR techniques have quantified variations in aliphatic, aromatic and heteroatom-bound carbon fragments, demonstrating that traditional structural parameters tend to underestimate maturity and overestimate generative potential in certain shale types. The resulting improved model equations, informed by precise molecular metrics, offer enhanced maturity assessment and hydrocarbon potential prediction applicable to a broad range of shales sharing similar depositional histories.

Characterization of Kerogen Structures in Oil Shales publication trend

The graph below shows the total number of articles in characterization of kerogen structures in oil shales across all publications each year (not limited to Nature Index journals).

Technical terms

Kerogen: The insoluble organic fraction of sedimentary rocks, comprising macromolecular structures that yield hydrocarbons upon thermal breakdown.

Thermal Maturity: The degree of chemical alteration of organic matter under geological temperature and pressure, commonly gauged by vitrinite reflectance.

Solid-State 13C NMR: A spectroscopic method that quantifies carbon functional groups and aromaticity in solid organic materials.

Reactive Force Field (ReaxFF): A computational framework enabling dynamic simulation of chemical reactions by allowing continuous bond formation and cleavage.

Macromolecular Model: A representative three-dimensional construct of kerogen’s atomic architecture used to study structure–reactivity relationships.

References

1. The Constructions and Pyrolysis of 3D Kerogen Macromolecular Models: Experiments and Simulations. Global Challenges (2019).
2. Improved Kerogen Models for Determining Thermal Maturity and Hydrocarbon Potential of Shale. Scientific Reports (2018).
3. Structural characterization of Huadian oil shale kerogen by using 13C DP/MAS NMR. Oil Shale (2021).
4. Three-dimensional molecular modeling of Dachengzi oil shale kerogen. Oil Shale (2022).