APPLICATION OF CARBOXYLIC-ACID BIOMARKERS AS INDICATORS OF BIODEGRADATION AND MIGRATION OF CRUDE OILS FROM THE MARACAIBO BASIN, WESTERN VENEZUELA

The acid fractions of 15 crude oils of different degrees of maturity, biodegradation, and origin, from the Maracaibo Basin, western Venezuela, were analyzed by high-resolution ps chromatography/mass spectrometry (GC/MS) to determine their usefulness as indicators of biodegradation and oil migration. Acyclic as well as tri- and pentacyclic (hopanoic) monocarboxylic acids were identified and quantified for this purpose. The total acidity as well as the ratio of tricyclic to pentacyclic acids were good parameters of biodegradation in these oils. When used in conjunction, they differentiated ''mixed'' oils (biodegraded with non-biograded) and early generated oils from others. Contrary to previous reports, hopanoic acids (HAs) were found to be more resistant to biodegradation than, their alkane counterparts. The isomeric distribution of the HAs as well as the carbon preference index (CPI) and the C28/C18 ratio of the n-acids were found to be useful in determining the migration histories of the oils.