Raman Spectroscopy Applications in Organic Maturity Assessment

Raman spectroscopy has emerged as a cornerstone technique for assessing the thermal maturity of organic matter in geological materials. By probing the vibrational modes of carbonaceous structures, Raman analysis yields characteristic D-band and G-band signatures that reflect the degree of aromatisation, disorder and graphitisation within kerogen, bitumen and dispersed organic macerals. These spectral metrics can be correlated with conventional maturity indicators such as vitrinite reflectance and pyrolysis Tmax, offering a rapid, non-destructive complement to established methods. Applications span evaluation of source-rock thermal histories, prediction of hydrocarbon generation windows and mapping of maturity gradients across sedimentary basins. Recent advances in multivariate spectral deconvolution and machine-learning have improved reproducibility and reduced operator bias in peak-fitting procedures, while single-particle approaches permit targeted analysis of individual macerals. However, challenges remain in standardising protocols for fluorescence suppression, kinetic interpretation under varying heating rates and distinguishing strain-induced spectral changes from purely thermal effects. Overall, Raman spectroscopy is poised to become an integral part of multidisciplinary workflows for hydrocarbon exploration and organic geochemistry, with potential extensions to planetary science and materials research.

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Technical terms

Raman spectroscopy: A vibrational spectroscopic method that probes molecular bonds by inelastic scattering of monochromatic light, yielding information on structural order and chemical composition.

D-band: A Raman feature near 1,350 cm⁻¹ indicative of disorder and defects in sp² carbon networks, sensitive to the presence of non-aromatic and edge structures.

G-band: A Raman feature near 1,580 cm⁻¹ arising from the in-plane stretching of sp²-bonded carbon, correlated with graphitic order and aromaticity.

Vitrinite reflectance: A petrographic measure of the percentage of incident light reflected by vitrinitic macerals, widely used as a thermal maturity proxy in sedimentary rocks.

Kerogen: The insoluble organic fraction of sedimentary rocks, comprising a complex mixture of hydrocarbons and biomacromolecules that generate oil and gas upon thermal maturation.

References

1. Towards a kerogen-to-graphite kinetic model by means of Raman spectroscopy. Earth-Science Reviews (2023).
2. Spectral narratives of microstructural restyling and their controls on hydrocarbon generation potential from coal. International Journal of Coal Science & Technology (2023).
3. Compositional evolution of organic matter in Boquillas Shale across a thermal gradient at the single particle level. International Journal of Coal Geology (2021).