LAUSR

Abstract— One of the processes that can locally be involved in forming the composition of aromatic hydrocarbons in oils is the reaction of electrophilic methylation of aromatic cycles. Up to 40% of the original oil compounds can be transformed into methylation products. Methylation is demonstrated to most likely proceed during catagenesis, after the generation of the fluid that had produced a given oil accumulation. The methylation of aromatic cycles is a definite indicator that the source rocks are either clays or silicites containing relatively much clay material. The methylation reaction is proved not to be widespread even within a given basin, and hence, analysis for the presence of electrophilic methylation products can be efficiently applied in geochemical reconstructions. One of the consequences of methylation may be changes in the concentrations of isomers of aromatic compounds that are used in calculating maturity coefficients, and this may lead to misinterpretations of the results.