Kerogen kinetics and the effect of rock matrix: Insights from Western Greece

Abstract

The importance of kerogen kinetics extends beyond hydrocarbon generation, encompassing thermal modeling, organic matter heterogeneity, and the assessment of thermal decomposition. Our study focuses on analyzing the organic and inorganic signatures of source rock intervals, by integrating also literature maceral compositions, to identify potential correlations between kinetics and the mineral matrix. To achieve this, nineteen samples from proved Mesozoic source rock intervals in Western Greece were analyzed. Rock-Eval 6 pyrolysis experiments identified thermally immature to slightly mature, mainly type II, and mixed I-II kerogens. X-ray fluorescence and X-ray diffraction analysis revealed a predominance of carbonate over silicate minerals, indicating a carbonate-dominated source rock character and predominantly reducing marine depositional conditions. High sulfur contents, primarily observed in the Late Triassic – Early Jurassic interval, suggest euxinic conditions and the presence of II(S) kerogens. Bulk rock kinetic analysis revealed activation energy distributions mainly ranging from 43 to 60 kcal/mol. The Late Triassic – Early Jurassic and Early – Mid Jurassic intervals show greater heterogeneity with broad distributions, while the Mid – Late Jurassic and Early Cretaceous intervals exhibit more homogeneity, with two to three principal activation energy peaks. Kerogen isolation revealed differences in activation energies and frequency factors between the bulk rock and the kerogen, with the mineral matrix potentially having a minimal effect in the reaction rate. This research offers insights into the bulk kinetics of marine source rocks linked with global oceanic anoxic events, with broader implications to the hydrocarbon exploration in the fold and thrust belt of Western Greece, and to analogue geological settings worldwide.