Thermal Maturation of Organic-Rich Shales

Thermal maturation of organic-rich shales encompasses the progressive chemical and physical transformations undergone by kerogen and associated mineral assemblages as burial temperature and pressure increase. This process governs the generation and expulsion of hydrocarbons, the evolution of pore networks, and the transformation of clay and other mineral phases. In early diagenesis, organic matter retains hydrogen-rich structures that favour liquid hydrocarbon production during the oil window. As maturity advances into the gas window, cracking of residual hydrocarbons and secondary cracking of solid bitumen enlarge nanopore systems and alter pore connectivity. Concurrently, clay minerals may transform (for example, smectite to illite), and compaction reduces intergranular space, so the balance between pore creation and pore destruction determines overall porosity and permeability. The distribution of pore sizes—from subnanometre micropores to mesopores and larger microfractures—controls both hydrocarbon storage capacity and fluid flow. Understanding these coupled geochemical and geomechanical processes is essential for effective evaluation of shale reservoirs, optimisation of production strategies and assessment of carbon sequestration potential in unconventional settings.

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Thermal Maturation of Organic-Rich Shales publication trend

The graph below shows the total number of articles in thermal maturation of organic-rich shales across all publications each year (not limited to Nature Index journals).

Technical terms

Kerogen: The insoluble organic fraction of sedimentary rock that generates hydrocarbons upon thermal maturation.

Total organic carbon (TOC): The proportion of organic carbon in a rock, indicating the quantity of potential hydrocarbon precursor.

Vitrinite reflectance (Ro): A measure of the maturity of organic matter, based on the reflectivity of vitrinite macerals under microscopy.

Nanopore: A pore with dimensions in the nanometre range (typically < 100 nm), critical for gas adsorption and storage in shale reservoirs.

Porosity: The fraction of a rock’s volume occupied by void spaces, which governs fluid storage and flow capacity.

References

1. Evolution of nanopore structure in lacustrine organic-rich shales during thermal maturation from hydrous pyrolysis, Minhe Basin, Northwest China. Energy Exploration & Exploitation (2017).
2. Porosity model and pore evolution of transitional shales: an example from the Southern North China Basin. Petroleum Science (2020).
3. A Review of the Heterogeneity of Organic-Matter-Hosted Pores in Shale Reservoirs. Energies (2022).