Maturity trends in asphaltenes from pyrolysed source rocks and natural coals—multivariate modelling of diffuse reflectance Fourier-transform infrared spectra

DRIFT spectra of asphaltenes have been modelled by multivariate methods to show the patterns of maturity dependent changes in chemical composition. The asphaltenes are from source rocks that have been artificially matured by hydrous pyrolysis, and cover a wide range of kerogen types and maturity levels. Asphaltenes from a set of naturally matured coal samples are modelled for comparison. The modelling results in defining a limited number of systematic trends in maturity dependent chemical changes in the spectra. The trends are comparable for similar source rocks and are interpreted as representing defunctionalisation, aromatisation and cracking reactions. However, the timing and maturity dependence of the reactions are specific for each source rock, and a general maturation model that includes all source rock types could not be established.