Ultraviolet-fluorescence alteration of hydrocarbon fluid inclusions

Abstract

Ultraviolet fluorescence emission spectra were recorded on natural and synthetic hydrocarbon fluid inclusions. Trapping and heating of oil inside the inclusions causes a red shift and a decrease of the fluorescence intensity. The thermal alteration of the fluorescence varies with the expansion of the inclusions. When the inclusions are expanded by non-isochore evolution with temperature, the fluorescence alteration is positive. The alteration of fluorescence with time induces irreversible changes in inclusions trapped in salt crystals: the intensity of the fluorescence emission and the red/green ratio increase. Analysis by FT-IR microspectroscopy was performed before and after u.v. treatment at 300°C for 4h. The preexisting conjugated ketones are totally consumed to produce aryl-ethers and carbon dioxide. However, the alteration of fluorescence is more sensitive to chemical changes than i.r. spectroscopy. There is no significant alteration for inclusions trapped in quartz crystals; no temporal alteration is detected, the thermal alteration cannot be recorded because of decrepitation, and the i.r. spectrum is masked by the spectrum of quartz. The alteration of the fluorescence of the inclusions depends both on the nature of the oil and on the nature of the host crystal. The alteration parameter can be used for the characterization of the oil inclusions and indication of oxidation state.