Characterization of asphaltic oil occurrences from the southeastern margin of the Basque-Cantabrian Basin, Spain

A geochemical investigation has been undertaken on biodegraded hydrocarbons in outcropping reservoirs of the south-eastern margin of the Basque-Cantabrian Basin (Álava sector). The aims of the study were the characterization of the geochemical features and biodegradation level of these hydrocarbons,...

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Bibliographic Details
Published in:Acta geologica hispanica 2014, Vol.12 (4. ALAGO Special Publication: Selected Contribution from the XIII Congress), p.327-343
Main Authors: Marín, P., Márquez, G., Gallego, J.R., Permanyer, A.
Format: Article
Language:English
Subjects:
Aromatic compounds
Asphaltic oil occurrences
Ayoluengo oil field
Basque
Basque Country
Basque-Cantabrian Basin
Biodegradació
Biodegradation
Cantabria
Cantabrian basin
Cantàbria
Carbonate rocks
Gas chromatography
Geochemistry
Hydrocarbons
Mass spectrometry
null
Oil and gas fields
País Basc
Álava sector
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Summary:A geochemical investigation has been undertaken on biodegraded hydrocarbons in outcropping reservoirs of the south-eastern margin of the Basque-Cantabrian Basin (Álava sector). The aims of the study were the characterization of the geochemical features and biodegradation level of these hydrocarbons, and the evaluation of their resemblance to oils from the Ayoluengo onshore oil field by means of isotopic analyses and gas chromatography-mass spectrometry techniques. Most of the samples lack n-alkanes, isoprenoids, low molecular weight aromatic compounds, steranes, homohopanes, diasteranes and triaromatic steroids, whereas hexacyclic and heptacyclic alkanes appear as key compounds although some structures were not totally elucidated. Thermal maturity has been assessed with several parameters and a calculated-equivalent vitrinite reflectance value of around 0.8% was estimated. In addition, gammacerane content, diasterane-to-sterane ratio and C35 to C34 hopanes ratio suggest that the Álava oil shows were derived from a carbonate rock deposited in a reducing, water-stratified and possibly hypersaline environment. Isotopic signatures and other data confirmed that these hydrocarbons are not genetically related to the oils from Ayoluengo and, consequently, their origin is associated with a yet unknown source rock in the basin.
ISSN:1695-6133
0567-7505
1696-5728
DOI:10.1344/GeologicaActa2014.12.4.4