Environmental Forensics Study of Crude Oil and Petroleum Product Spills in Coastal and Oilfield Settings: Combined Insights from Conventional GC-MS, Thermodesorption-GC-MS and Pyrolysis-GC-MS

A representative set of five oil spill samples from four different regions displayed different product characteristics and different levels of weathering. Three of them were taken along shorelines affected by marine oil spill events, viz., Aboño and Prestige (Spain) and Deepwater Horizon (USA) and the other two were taken at inland oil spill sites (Angola and Kuwait). A multi-faceted environmental forensics approach revealed key molecular features. In addition to the conventional GC/MS analysis of saturated and aromatic fractions, the polar fractions also were analyzed, revealing a complex series of linear alkanones in those oil samples particularly enriched in aliphatics. Thermodesorption-GC-MS of the whole oils was also employed to further test its efficacy as a tool for the rapid fingerprinting of environmental contamination. The method was shown to accurately detect most of the essential features recognized in the conventional GC-MS analysis of the saturated and aromatic fractions, although in some instances with less sensitivity and poorer resolution. Characteristics so recognized included the distributions of normal and isoprenoid alkanes, saturate and aromatic biomarkers, and polycyclic aromatic compounds such as alkylphenanthrenes and alkyldibenzothiophenes. Sequential pyrolysis of the post-thermodesorption residue and asphaltene pyrolysis yielded similar results, indicating that the residue consists primarily of asphaltenes. Thermodesorption and pyrolysis GC-MS also recognized substances likely to be associated with spill cleanup efforts that were not detected by conventional analysis

Técnicas avanzadas para la caracterización de petróleos pesados, productos derivados y sus fracciones : aplicaciones en ingeniería de yacimientos y medio ambiente

En un mundo donde las energías fósiles continúan hoy día jugando un papel crucial, las compañías petroleras siguen evaluando la viabilidad económica de yacimientos de petróleo crudo no convencional a fin de asegurar las necesidades energéticas de la población. En este contexto, los petróleos pesados y extrapesados constituyen una parte importante de las reservas mundiales de hidrocarburos, cuya explotación conlleva considerables problemas técnicos y riesgos medioambientales. La problemática ligada a las fracciones pesadas del petróleo crudo explica muchas de las dificultades presentadas durante la explotación de hidrocarburos. Por otro lado, a pesar de la disminución de vertidos petroleros durante las últimas décadas, los vertidos derivados de las tareas de extracción y transporte de petróleo siguen poniendo en peligro los ecosistemas marinos y terrestres. Las fracciones pesadas del petróleo y sus derivados generan serias dificultades en la recuperación de terrenos afectados por vertidos como resultado de la dificultad que presentan estas fracciones a ser meteorizadas o biodegradadas. La caracterización de estas fracciones polares o de crudos pesados no es una tarea sencilla, dado que el procedimiento analítico de las macromoléculas que constituyen la fracción asfalténica es muy complejo. Así, el desarrollo de protocolos analíticos para realizar la caracterización de productos enriquecidos en las fracciones polares resulta completamente necesario. El protocolo propuesto en esta tesis ha permitido elucidar los mecanismos de formación de los “tarmats” en los yacimientos considerados. En el caso de las muestras de vertidos costeros, el protocolo ha posibilitado realizar un seguimiento de la evolución de la atenuación natural de los mismos, así como establecer que la técnica TD/GC-MS es un método de caracterización rápida de los vertidos en combinación con otras técnicas pirolíticas. Los resultados han permitido también establecer grupos de petróleos pesados genéticamente diferentes en campos como los estudiados en Los Llanos (Colombia) y Ceuta (Venezuela). Además, se ha podido identificar los mecanismos que han dado lugar a la formación de “tarmats”, así como establecer correlaciones crudo-crudo y crudo-roca madre. Por último, se concluyó que el principal factor que controla la atenuación natural son los ciclos climáticos estacionales, viéndose la misma ralentizada al final de los periodos estivales. Además, se establecieron varios ratios diagnósticos basadas en compuestos saturados con el fin de discernir los diferentes tipos de meteorización. Los ratios basados en compuestos aromáticos, sin embargo, solo permitieron una aproximación cualitativa a la meteorización, sin distinguir entre biodegradación, volatilización y fotodegradación. La pirolisis secuencial de muestras sin fraccionar de vertidos petroleros se puede usar como herramienta de identificación rápida, puesto que se ha observado que el análisis CG-MS del producto de la desorción térmica permite identificar de manera bastante clara los mismos compuestos que se identifican empleando el análisis CG-MS de las fracciones saturada y aromática. Como consecuencia, el residuo de la desorción térmica solo contiene principalmente asfaltenos, como demuestra que en sus pirocromatogramas se observan los mismos picos que en el caso de la pirólisis de la fracción asfalténica.Nowadays, fossil fuels still play a crucial role. As a result, oil companies are exploring the economic viability of non-conventional oil fields to ensure population energy needs. Heavy oils and extra heavy oils signify an important part of the oil reserves worldwide. Their exploitation implies technical problems and environmental risks, and therefore the problematic linked to the oil heavy fractions generates difficulties in hydrocarbons production. Despite the positive trends in the reduction of oil spills, they continue to put marine ecosystems at risk, as well as terrestrial ecosystems, when there are accidents during exploration, extraction or transportation. Heavy oil fractions, in this case, generate serious difficulties in the recovery of land affected by discharges, both marine and terrestrial environments. This is due to the resistance of these fractions to weathering and biodegradation. Heavy oils, and its heavy fractions are not easy to characterize. Difficulties are mostly related to asphaltenes, which are relatively abundant molecules in oil with a very complex analytic. In this context, it is necessary the development of analytical protocols that facilitate heavy oil characterization, and this is the main scope of this thesis. The proposed protocol has revealed the intra reservoir "tarmats" formation mechanisms. In coastal oil spills, the protocol gave the possibility to follow the natural attenuation in the environment. It was also revealed that TD/GC-MS is a rapid forensic tool in combination with pyrolytic analysis. Some of the specific results obtained in the applied cases developed in this work elucidated genetically different oil groups in fields affected with heavy oils in Los Llanos (Colombia) and Ceuta (Venezuela). Moreover, we have been able to identify oil mixing, as well as explaining the "tarmats" formation mechanisms. Finally, it has been possible to identify the oil-oil and oil-source rock correlations thanks to simultaneous analysis of rock, oil and "tarmats". On the other hand, in the context of environmental studies, seasonal climate cycles were shown as the main factor controlling natural attenuation advances after an oil spill, In addition, some diagnostic ratios using saturate compounds were selected to distinguish between distinct types of weathering and aromatic ratios were also useful to obtain a qualitative approach although without distinguishing between biodegradation, volatilization and photodegradation. The sequential pyrolysis of spilled products may be use as a rapid forensic tool, since the compounds identified by GC-MS of thermally desorbed products are identified as well those in saturated and aromatic fractions. In addition, the thermal desorption residue is predominantly asphaltenic, as revealed by the thermal desorption product pyrochromatogram (very similar to the asphaltene pyrochromatogram)