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Modelling and kinetic analysis of the thermal maturity of kerogen in Western Greece and its correlation to the prevailing palaeoenvironmental conditions

Makri Vagia-Ioanna

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Summary

The fold-and-thrust belt of Western Greece preserves a succession of Mesozoic organic-rich intervals that vary in depositional environment, geochemical character, and hydrocarbon generation potential. This thesis investigates the mineralogical, geochemical, and kinetic properties of these intervals through the integration of XRD, XRF, Rock-Eval, biomarker, and palynofacies data, combined with 1D thermal modelling.Mineralogical analysis indicates a predominantly carbonate-rich character throughout the stratigraphy, with dolomite prevailing in Late Triassic – Early Jurassic samples and calcite dominating the younger units. Elemental geochemistry and redox-sensitive trace elements reveal evolving depositional conditions through time. Arid settings and euxinic conditions dominated the Late Triassic – Early Jurassic intervals, transitioning to more variable redox regimes with enhanced anoxia during the Jurassic and Early Cretaceous.Organic geochemical and palynological data indicate a range of kerogen types, mainly from Type II to II(S). Total organic carbon (TOC) reaches 35.56 wt% and Hydrogen Index (HI) values up to 728 mgHC/gTOC, while most samples remain thermally immature to early mature. Amorphous organic matter dominates, whereas increased sporomorph and phytoclast input in some units reflects terrestrial influence, affecting both preservation and kerogen reactivity. These variations are stratigraphically coherent and control kinetic behavior and generation profiles.Kinetic modelling demonstrates that activation energy (Ea) distributions vary with age and facies. Late Triassic – Early Jurassic and Early – Middle Jurassic samples show broad Ea-distributions with two to three principal peaks, covering 58–94% of the total generation potential, indicating chemically heterogeneous kerogens and gradual transformation profiles. In contrast, Mid – Late Jurassic and Early Cretaceous samples display narrower Ea-distributions, with up to 95% of potential concentrated in one or two peaks, consistent with more homogeneous kerogen and sharper generation windows. Organic sulfur content reduces Ea values and enhances reactivity, whereas calcite-rich matrices may moderate it.1D thermal modelling of the AY-3 and PxGa-1x wells underscores the critical influence of kinetic model selection on hydrocarbon generation predictions. Differences in TR10 values between custom and library kinetics result in depth shifts exceeding 1 km under a uniform geothermal gradient. Custom kinetics yield lower TRmax and delayed hydrocarbon generation, whereas library kinetics often overestimate maturity, particularly in shallow or structurally complex intervals. Burial and thermal history calibration using vitrinite reflectance and biomarker ratios provide additional constraints on uplift, erosion, and structural evolution, suggesting eroded intervals exceeding 1 km of thickness.This study highlights the mineralogical and kinetic complexity of Mesozoic source rocks in Western Greece and the necessity of custom kinetic models for accurate simulations. These findings improve our understanding of organic matter reactivity in carbonate-rich fold-and-thrust belts and enhance hydrocarbon system prediction in analogous geological settings.

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