Identificação de derrames de óleo no mar: um estudo de caso

Abstract

Petroleum is one of the most important energy sources known. In Brazil, oil is mainly extracted from offshore wells. Because of the characteristic s of the brazilian oils, the great distances between the main productive areas and industrial processi ng and consumption centers, and because of the refining processes adopted in Brazil, the traffic of ships carrying oil or derived products is common. Oil spills frequently occur, with var iable damage to the environment, sometimes without the identification of responsible parties . In the marine environment, such oil spills can be caused by human or equipment errors in ships, harbours, petroleum platforms and their support facilities, by irregular c rude oil washing on tankers or by disposal of used oils. An oil spilled in the sea, is subject t o weathering, an assembly of several natural phenomena that promote degradation of the oil, modifying its composition and, finally, removing it from the water surface. Even so, damage ef fects can persist in the affected area for a long time, depending, among other factors – on the original oil composition. Various techniques have been developed for identification of oil spills in the s ea, each one searching to unambiguously identify the source of the spil l, even when the released oil has been subjected to weathering. This work represents a Case Study where advanced geochemical techniques for oil spill fingerprinting were used, incl uding manual and automated data interpretation, aiming to identify and characterize the source of an oil spill in the brazilian coast, occurred in september, 2005. By GC-FID profile of the oils, it was concluded that the spilled oil in the São Marcos Bay, city of Sã o Luís – MA, was slightly weathered crude oil. The spilled oil and suspected vessels were st ill investigated by “whole oil” isotopic ratio mass spectrometry, nickel and vanadium determi nation and, mainly, by their GC-MS biomarkers profile. It was possible to distinguish, base d both on the high correlation capabilities of some geochemical parameters as w ell as multivariate analysis of several developed diagnostic ratios, that one sample was very sim ilar to the spilled oil. The corresponding ship was the only one, among the suspected vessels, that could have caused the incident. By comparison of the spilled oil with geochemical propertie s accepted in the literature to correlate oil and source-rock, it was concluded that the oil found in São Luís was generated from a marine carbonatic source rock. The high concentrat ion of vanadium and the high V/Ni, unusual in brazilian oils, as well as the high concentrat ion of tricyclic terpanes, eliminated the chances of being a brazilian oil and suggested it could have been imported from Venezuela, one of the biggest oil producers and known by their oils w ith high vanadium concentrations. The presence of oleanane, although much less abundant tha n C 30 αβ -hopane, allied to other characteristics, has confirmed that the spilled oil in São Marcos Bay was imported.