The fluorescence behaviour of crude oils with respect to their thermal maturation and degradation

Abstract Quantitative spectral fluorescence measurements were made on 45 crude oils and condensates of various origins and ages, whose physical properties and gross chemical composition differed widely. To characterize their fluorescence behaviour, measurements were made at a fixed wavelength irradiation of 365 nm, where the oils were spread as a thin layer on glass slides covered with Kieselguhr G. The emission spectra were recorded from 420 to 700 nm in steps of 5 nm. With increasing maturation of the oils a continuous shift from a maximum wavelength of 550 nm (green-yellow) to 440 nm (blue) occurred. The negative alteration, after an exposure time of 30 min amounted to more than 75%. Heavy, degraded oils were shown to have their maximum intensity at wavelengths between 590–610 nm, i.e. in the yellow-orange region, and tended to have a lower negative alteration. Fluorescence methods are suitable to distinguish the different stages of thermal maturation and degradation in crude oils and condensates.