Abstract:

       This study proposed a method to distinguish the bio-precursors of organic matter in hydrocarbon source rocks. Through
analysis of the Raman spectra of two common types of organisms, phytoplankton and benthic algae, in hydrocarbon source rocks, we found that the organic matter originated from different organisms have different Raman spectra characteristics. The difference in Raman shift between G-mode peak and D-mode peak normally indicates the polymerization degree of aromatic structures, and the intensity ratio of D-mode peak to G-mode peak reflects the order degree of aromatic structures. By comparing the spectra parameters of different hydrocarbon-forming organisms, we found that the polymerization degrees of the macerals originated from benthic algae are greater than those of phytoplankton as well as the order degree of phytoplankton is also greater than benthic algae. Our research shows that the difference in Raman shift between G-mode peak and D-mode peak of different hydrocarbon organisms sampled from the same layer displays significant difference. The polymerization degree of aromatic structure of organic matter can be detected by Raman spectroscopy to distinguish different organisms. Although the intensity ratio of D-mode peak to G-mode peak is not only subject to the thermal maturity of materials but also sensitive to their structure properties of bio-precursor organism, it may also serve as a reference for distinguishing different hydrocarbon-forming organisms in practice.

Key words: Raman spectroscopy, order of aromatic organic matter, hydrocarbon-forming organisms