Acidic biomarkers from Albacora oils, Campos Basin, Brazil

Acidic biomarkers of 8 different oil samples from Albacora oil field, Campos Basin, Brazil, were analyzed in order to obtain additional information about biodegradation and thermal evolution. For this purpose, we selected oils (lacustrine saline origin) showing different biodegradation levels and at different distances from the fault that acted as migration pathway in the area. Previous analyses using hydrocarbon biomarkers suggested a mix of oil charges, characterizing two distinct oil cycles interrupted by meteoric water circulation in these reservoirs. Analyses of the naphthenic acid biomarkers revealed a parallelism between the hydrocarbon and the acidic biomarkers. Notwithstanding, there is evidence that the carboxylic acid biomarkers, more resistent to biodegradation, can provide information on past reservoir history when most important neutral biomarkers have been biodegraded. The limitations to the use of these biomarkers are their "de novo" synthesis in the biodegradation process and the complexity of the sample manipulation prior to the analysis. (C) 1999 Elsevier Science Ltd. All rights reserved.