Characterization of organic matter generated from Green River shale by infrared laser pyrolysis

Abstract

An infrared (CO₂) laser micropyrolysis system for analyzing organic matter in rock was developed and applied to a Green River shale sample. A series of n-alkanes (C₈–C₃₃), isoprenoids (C₁₈–C₂₀), triterpenoids (C₂₇–C₃₁), and steranes (C₂₇–C₂₉), as well as β-carotane (C₄₀), were detected as the main compounds in the laser pyrolysates without serious degradation. These results indicate that infrared laser micropyrolysis is superior to short-wavelength laser micropyrolysis in determining the original molecular composition of organic matter in a rock sample. By comparing the infrared laser pyrolysates with the solvent-extractable organic matter from the shale and the conventional flash pyrolysates of the macromolecules (kerogen) in the rock, we concluded that the infrared laser pyrolysates come from thermal evaporation of solvent-extractable organic compounds and pyrolytic fragmentation of the macromolecules. Roughly equal amounts of the thermal extracts of bitumen in the sample and the pyrolysis products were produced under the experimental conditions.