Characterization of chemical structure, degree of maturation and oil potential of Torbanites (type I kerogens) by quantitative FT-i.r. spectroscopy

Abstract

The kerogen of Torbanites of various origins (natural and laboratory-heated samples) was examined by quantitative Fourier transform infrared spectroscopy (FT-i.r.). This study was carried out from difference spectra, obtained by low temperature ash (LTA) subtraction, or from deconvoluted regions of such spectra. The various indexes thus obtained allowed for determining the degree of natural and artificial evolution of Torbanites and the associated changes in chemical structure; comparing artificial versus natural evolution; and assessing the oil potential retained by matured Torbanite samples. The scopes and limitations of these FT-i.r. indexes were considered and compared with those of previously used methods. Quantitative FT-i.r. thus appears more efficient than elemental analysis or microspectrofluorimetry (in assessing the degree of natural evolution, in the first and last steps of maturation, respectively) and than solid-state 13C nuclear magnetic resonance (n.m.r.) (in showing the relative enrichment in ether groups during evolution). When kerogen isolation via demineralization is performed, prior to i.r. examination, the drastic acid treatments then required may alter the chemical structure of organic matter; such a drawback is not encountered in studies based on LTA preparation and difference spectra.