A PRACTICAL APPROACH TO QUANTITATIVE GROUP TYPE ANALYSIS OF KEROGENS USING NON-DEDICATED PYROLYSIS MASS-SPECTROMETRY EQUIPMENT - APPLICATIONS AND COMPARISON WITH OTHER METHODS

Pyrolysis-mass spectrometry (Py-MS), based on a slight modification of a non-dedicated MS, has been applied to the quantitative determinatio n of different groups of hydrocarbons and non-hydrocarbons present in kerogen pyrolysates. The Py-MS experiments were carried out by using c onventional pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) equipment where the pyrolysate enters the ion source directly via an e xpansion chamber. A suite of kerogens were flash pyrolysed at 700 degr ees C for 20 s and the mass spectral data of the pyrolysates were acqu ired at low electron voltage (20 eV), scanning from m/z 30 to 250. Ela psed analysis time is approximately 2-3 min for each kerogen sample. M edium resolution (2500 RP) was applied to reduce the nominal mass over lap and thus enhance the identification potential. Quantification of t he pyrolysate compounds was achieved by adding an internal polymer sta ndard to the samples, accompanied by the use of response factors for e ach compound class, established by analysis of reference compounds. Th e Py-MS results have been evaluated in comparison with data from other analytical methods (Rock Eva1 pyrolysis, combined microscale sealed v essel pyrolysis-gas chromatography (MSSV-Py-GC), elemental analysis, n uclear magnetic resonance spectroscopy, high resolution MS of pyrolysa tes). The Py-MS method appears to be a reproducible and rapid techniqu e for evaluation of sedimentary organic matter. Py-MS data and results from conventional and other analyses mentioned above were correlated using multivariate analysis. Good correlations between pyrolysate yiel d parameters from Rock Eva1 pyrolysis, MSSV-Py-GC and atomic H/C conte nt from elemental analyses of kerogens versus hydrocarbon yields measu red by Py-MS, are observed. The Py-MS pyrolysate yields and the relati ve aromatic hydrocarbon content clearly differentiate between kerogens with the high (> 1.4), intermediate (0.5-1.4) and low H/C ratios (< 0 .5), when multivariate processing was applied. Kerogens with atomic H/ C ratios between 0.5-1.0 are separated from those with H/C ratios betw een 1.0-1.4, mainly by differences in the alkylthiophene and carbon di oxide yields as well as the relative amount of different classes of hy drocarbons. In addition, there was a good correlation between Py-MS pa rameters and a variety of parameters obtained by other pyrolysis techn iques widely in use in the petroleum industry. Thus, gas to oil ratios determined by sealed vessel pyrolysis GC correlate negatively with e. g. the relative amount of cycloalkanes present in pyrolysates as measu red by Py-MS. Finally, the mean aikyl chain length in the kerogens has been estimated from pyrolysate Py-MS data based on calibration of MS- fragmentation ratios (m/z 43/85) against known alkyl chain lengths.