Migration and Biodegradation of Hydrocarbons in the Potiguar Basin, Brazil: Assessment by Trace Elements Determination in Crude Oils and Fractions by ICP-MS

Dreyfus, S.¹, C. Pecheyran¹, C.P. Lienemann², C. Magnier³, L.A.F Trindade⁴, A. Prinzhofer⁵, O.F.X. Donard¹ (1) LCABIE / CNRS UMR 5034, Pau, France (2) Institut Francais du Petrole, Vernaison, France (3) Geology-Geochemistry, Institut Francais du Petrole (4) CENPES, Petrobras, Brazil (5) Institut Francais du Petrole, Rueil-Malmaison Cedex, France

In the recent years, intensive studies have been dedicated to the geochemical character­ization of petroleum systems. Trace and ultra trace metals in crude oils may be used as geo­chemical markers in oil-oil and oil-source rock correlations, identification of source rocks depositional environment and in the quantification of oils thermal maturity and biodegrada­tion levels. Elemental signatures such as Ni and V concentrations evolution in crude oils have already been used to determine the degree of reservoir biodegradation. However new parameters are needed to improve the general knowledge about migration, maturation, mix­ing and biodegradation of the oil from an inorganic or bioinorganic angle. Sensitive meth­ods are then required to analyze other elements occurring in petroleum in very low concen­tration (like Mo, Pb, Cu, Cd, Sn, Ba,…). The instrumental limitations of the most common techniques used so far (AAS, ICP-OES), have been the main reason for the poor knowledge about inorganic constituents of crude oil. Performances of the inductively plasma mass spectrometry allows now the detection of very low concentrations in an organic matrix. A method was developed to analyze directly trace and ultra-trace metal elements in crude oil and its fractions (maltenes, asphaltenes) by ICP-MS after sample dilution in xylene. Several biodegraded and non biodegraded crude oils and fractions originating from the Potiguar Basin (Nordeste, Brazil) have been analyzed. New elemental and isotopic tracers of matura­tion, mixing, or biodegradation have been identified. Results on elemental and isotopic dis­crimination as a tool of geochemistry will be presented.