Vibrational spectroscopy assessment of kerogen maturity in organic-rich source rocks

Source rocks are sedimentary rocks containing organic matter. In order to evaluate if a source rock is suitable for economical exploitation, the evaluation of many factors is required, among which the most important are concentration of the organic matter and its quality (e.g. kerogen type and thermal maturity) that evolves following temperature and pressure over burial history. The most commonly used techniques to characterize the thermal maturity of organic matter are the maximum pyrolysis temperature of generated hydrocarbons and the reflectance of vitrinite macerals (%Ro). The limitations to the applicability of these analyses is the driving force to develop new methods and in particular spectroscopic ones. In this work the maturity of different kerogens (i.e. solid organic matter entrapped into rocks), both naturally and artificially aged, is determined by Raman and Attenuated Total Reflection-InfraRed (ATR-IR) spectroscopies, applied directly to source rocks. The parameterization of spectra by suitable variables proved to allow evaluating kerogen maturity with the best reliability at lower rank for ATR-IR and at higher rank for Raman analysis. Good correlations were obtained between Raman and ATR-IR spectroscopic parameters and the above mentioned vitrinite reflectance (%Ro).