Alkylbiphenyls and alkyldiphenylmethanes as indicators of petroleum biodegradation

Gas chromatographic-mass spectrometric analyses of alkylbiphenyls and alkyl diphenylmethanes have been performed on a series of crude oils reservoired in the Gippsland Basin (Australia), as well as in some marine coastal sedim ents contaminated with a condensate. Changes in the isomeric distribution o f the alkylbiphenyls and alkyldiphenylmethanes with increasing biodegradati on were investigated. The relative abundance and distributions of the isome rs were found to change significantly with increasing biodegradation. Isome rs with the 4-substituent(s) generally increase in abundance relative to is omers that lack this feature. Thus, alkylbiphenyl and alkyldiphenylmethane isomeric distributions are useful indicators of the extent of petroleum bio degradation in reservoirs and surface sediments. It is suggested that geosy nthetic processes and/or relative susceptibilities of certain isomers to mi crobial attack can account for changes in the isomeric distribution of thes e components with increasing biodegradation. Significant differences in the relative abundances of the methylbiphenyls are apparent and are probably d ue to variations in the conditions that the petroleum had been subjected to in the two contrasting environments. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.