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APPLICATION OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) TO THE ASSESSMENT OF THERMAL MATURITY OF LOWER PALEOZOIC MARINE SHALEGold Open Access

Authors: X. Xu, W. Sun, C. Jiang, S. Wang, J. Qin, B. Shen and J. Yang
Event name: 29th International Meeting on Organic Geochemistry
Session: Posters - Source Rocks
Publication date: 02 September 2019
DOI: 10.3997/2214-4609.201902806
Language: English
Info: Extended abstract, PDF ( 314.13Kb )

Summary:
The Lower Paleozoic marine shale is the main focus for shale gas research in China, and one prominent challenge is to accurately evaluate the maturity of organic matter in these strata. There are no higher plant related macerals in these strata, so the classical vitrinite reflectance method cannot be applied. In addition, the thermal maturity of these strata are generally higher than 2.5% Ro according to previous studies, and thus existing methods such as bitumen reflectance, Rock-Eval Tmax, and biomarker isomerisation cannot accurately measure the maturity of organic matter. Therefore, it’s necessary to find alternative effective maturity evaluation method suitable for these strata. Previous research have shown that polycyclic aromatic hydrocarbons (PAHs) can be used to predict the maturity order for sedimentary organic matter, especially for samples in the late-oil window and beyond based on their structural stability. However, there are few reports on the change of these compounds at maturity levels higher than 2.5% Ro. This study aims to use laboratory hydrocarbon generation simulation experiments combined with pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) analysis to tackle this problem. The results show that the maturation stage of organic matter can be determined according to the presence of different methyl substituents of PAHs. The methylphenanthrene index and ratios of methylnaphthalene/naphthalene and toluene/benzene can be used to calculate the equivalent vitrinite reflectance of organic matter. These findings indicate that the method has good application prospect in evaluating the maturity of shale at high maturity.

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