[Statistical Characteristics of Raman Shift of Petroleum Components Ⅰ: Alkanes and Aromatic Hydrocarbons]

Hydrocarbon inclusions play an important role in the study of petroleum-bearing basin in terms of the generation, migration and accumulation of hydrocarbons. It’s important to understand petroleum basin by determining hydrocarbon molecules in hydrocarbon inclusions. Laser Raman spectroscopy has been widely used as a non-destructive assay methods for individual fluid inclusion analysis. However, this method is restricted in two aspects of the application on the hydrocarbon inclusion. One is that the complexity of petroleum which molecular is difficult to be identified. Another is that the Raman signal is usually covered by the fluorescence of most hydrocarbon inclusion. This article summarizes Raman spectroscopic characteristics of chain alkanes (n-alkanes and iso-alkanes) and aromatic hydrocarbons. According to our statistical results, some important conclusions can be reached. The normal alkanes of carbon number more than 10 can be identified by three Raman bands at 1 438, 2 890 and 2 850 cm-1. Iso-alkanes (take C8H18 as an example) containing two chains can be identified by a stable strong Raman peak at 2 875 cm-1. The strongest Raman peak combination of C—C (1 450 cm-1) and C—H (2 875 cm-1) is the evidence of the iso-alkanes containing one chain. Aromatic hydrocarbon containing one benzene ring can be identified by stable Raman band 1 600 cm-1 with two peaks. The combination of strongest Raman peaks of 1 005 and 3 060 cm-1 is the evidence of the aromatic hydrocarbon containing single chain, while the strongest Raman peaks of 1 250 and 2 910～2 920 cm-1 are the evidence of the aromatic hydrocarbon containing three chains. Aromatic hydrocarbons containing two benzene rings can be identified by stable Raman bandat 1 600 cm-1 double peaks and a strongest Raman peaks at 3 060 cm-1. All these typical Raman bands can be used to identify alkanes and aromatic hydrocarbons. The Raman spectroscopy-meter with short wavelength exciting light (blue to ultraviolet light) can effectively avoid fluorescence interference.