Título: Evidence of terrestrial crude oils in Machete area of the Orinoco IOL belt (OPB) by PY-GC-MS, from asphalthenes and Biomarkers analysis

Autor: Reategui, K.; Martínez, A.; Galarraga, F.; Martínez, M.

Fuente: 8th Latin American Congress on Organic Geochemestry CD-ROM Memorias

Año: 2002

País de publicación: Colombia

Tipo de documento: CD-ROM Memorias

Resumen

Previous work (Casani, F. and Eglinton G. 1991; Alberdi, M. et.al., 1996; Tocco, R et al., 1996) done in The Orinoco Petroleum Belt showed that most of crude oil within the basin were originated from Querecual and San Antonio Formation, constituted by marine organic matter from Cretaceous time. However, some reserachers using V, Ni and S concentration reveal the presence of a new family of crude oil with different geochemical profile in relation to the rest of the crude oils present in the area under study (Machete area, Figure 1). The main objetive of this work was to determine by means of PY-GC-MS from asphaltenes and biomarkers analysis, the origin of the crude oils in the Machete area.

The results obtained (Table 1 and 2) indicated that two different type of oils are present: the first group shows, by PY-GC-MS of asphaltenes, a serie of geochemical characteristic such as n-alkene/n-alkane distribution with maximum between C23-C35, besides a series of phenols, (C1;C2) cresols compounds. This kind of oils also show the presence of cadalene and absence of n-alkanes of low molecular weight. The biomarkers analysis show absence of triciclic terpanes, with hopane/sterane ratio greater than 5, ? ? C29 greater than ? ? C27 sterane and abundant signal of 18? (H) Oleanano. More over the low concentration of sulphur organic compounds and the fingerprint of C31-C35 homohopanes and methyl dibenzothiophenes seems to corroborate a siliciclastic type of source rock deposited under oxic-suboxic conditions. The second type of oil were associated to marine organic matter deposited under anoxic conditions.

In general, the maturity and biodegradation level in most of the samples were found to be similar. Statistic analysis (Figure 2) done on the molecular products obtained from PY-GC-MS of asphaltene corroborate that two different family of oil are distinguish and this analysis also show some dispersion in one of this family of crude oils and it seems to indicate that little changes in the biodegradation levels or mixing of oil during secondary migration might took place.