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Published online July 1, 2021

Copyright © International Union of Geological Sciences.

Fluorescence alteration of oil inclusions under ultraviolet irradiation

by Xiuyan Liu, Honghan Chen, and Chunquan Li*

Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China

Correspondence to:E-mail: tiger_lcq@sina.com

Received: January 12, 2021; Revised: May 23, 2021; Accepted: May 23, 2021

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The fluorescence colors of oil inclusions can be influenced by many geological factors including thermal maturity. However, the ultraviolet (UV) irradiation during laboratory process can also induce a significant alteration in fluorescence spectra of oil inclusions, which is seldom considered when using fluorescence to classify oil inclusions. Four oil inclusions from the Maokou Formation in the central Sichuan Basin, China were performed continuous UV irradiation. Their fluorescence spectra were recorded over time. The vapor / liquid phase ratio was measured by a confocal laser scanning microscope (CLSM). The results reveal a generally irreversible alteration of oil inclusion fluorescence spectra. λmax shows long-time stable and instant mutation, whereas QF-535 and Q650/500 exhibit monotone increasing trend. Recorded λmax can represent the original based on spectral shape analysis, however, recorded QF-535 and Q650/500 require a regression model to predict original values. Besides, there is a potential change in vapor / liquid ratio of oil inclusion after long and intense UV irradiation. The conclusion is that the thermal maturity determination by fluorescence spectra of oil inclusions should be used with care, because the spectra are easily altered during petrography study before being recorded.