The applicability of asphaltene treatment (mild oxidation and pyrolysis) in the investigation of crude oils

Asphaltenes isolated both from crude oils and extracts of source rocks have been widely studied in order to characterize initial substrates more precisely (Bowden et al., 2006; Liao and Geng, 2002; Liao et al., 2006). In these studies, the distributions of saturated biomarkers (n-alkanes, steranes and terpanes) were studied in detail, whereas less attention was dedicated to aromatic hydrocarbons.

In our study, asphaltenes were isolated from two non-biodegraded oils, by precipitation using n-heptane, and subjected to a thorough extraction of adsorbed compounds using Soxhlet method during 72 h. Thereafter, they were treated by mild oxidation, using H2O2/CH3COOH (Ox 1) and NaIO4/NaH2PO4 (Ox 2) (Liao and Geng, 2002), and close system pyrolysis during 4 hours at the temperatures of 250 °C (Pyr 250) and 400 °C (Pyr 400). The obtained products were separated into saturated, aromatic and polar fractions using column chromatography. Oil maltenes underwent the same procedure. Saturated and aromatic fractions were analyzed by gas chromatography-mass spectrometry. The aim of this study is to check which of asphaltene treatment techniques, used here, shows the best similarity in distributions of biomarkers and aromatic hydrocarbons and in the values of corresponding parameters with those obtained for maltenes. In order to investigate a wide range of compounds in the products of asphaltene treatment and in maltene fractions, as well as the influence of maturity of crude oils on the results, two non-biodegraded oils of different maturity were used: immature Zr-4 oil from the Pannonian Basin, Serbia (calculated vitrinite reflectance, Rc in range 0.6 – 0.7 %) and mature SI oil from the Middle East (Rc = 0.8 – 0.9 %). Apart from the direct comparison of results, a mathematical method of least squares was also performed to confirm a degree of accordance of values for numerous geochemical parameters in the asphaltene treatment products and maltenes.