Markers for secondary reactions of migrated crude oil on carbonaceous surfaces

• Published in: Organic geochemistry Vol. 49; pp. 30 - 35
• Main Authors: Alexander, Robert, Berwick, Lyndon J., Nasir, Shagufta, Fazeelat, Tahira, Grice, Kliti
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.08.2012; Elsevier
• Subjects: activated carbon; basins; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; heating systems; Hydrocarbons; hydrogen; naphthalenes; petroleum; Sedimentary rocks; sediments; Soil and rock geochemistry; Stratigraphy; Australia; Eromanga Basin; Western Australia; Cooper Basin; Queensland Australia; Carnarvon Basin; crude oil; naphthalene; Australasia; thermal alteration; aromatic hydrocarbons; closed systems; benzene; phenanthrene
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2012.05.007

► Ethyl aromatics thermally stabilized when heated with tetralin on carbon surfaces. ► Hydrogen donors limit reaction of ethyl aromatics relative to methyl aromatics. ► Higher ratio of ethyl aromatics indicates secondary reactions of migrated crude oil. ► Secondary alteration of crude oil observed in some Australian sedimentary basins. A high abundance of ethyl substituted aromatic hydrocarbons (HCs) relative to their methyl counterparts is an unusual feature of some crude oils. Enhanced stability of ethyl aromatic HCs in the presence of tetralin was observed when individual ethylated compounds were heated with activated carbon in sealed tubes over a range of 170–340°C. In addition, conversion of the common distribution of alkyl aromatic HCs to an unusual distribution, containing a higher relative abundance of ethyl compounds, was demonstrated by way of closed system heating of the aromatic fraction of a crude oil in the presence of activated carbon. The conditions for this unusual process require the presence of hydrogen donor components, which selectively limit the reaction and depletion of ethylated compounds relative to methylated compounds. The phenomenon has been shown to occur for substituted benzenes, naphthalenes, phenanthrenes and biphenyls. Enhanced abundance of ethyl aromatic HCs relative to their methylated counterparts is therefore proposed as an indicator for secondary reactions of migrated crude oil that has undergone thermal alteration after contact with carbonaceous surfaces in sediments. Application of these principles to selected crude oils and sediment extracts from the Carnarvon and Cooper/Eromanga Basins (Australia) indicates that significant secondary reaction of migrated crude oil has occurred.