Geochemistry of the hydrocarbons from the Orinoco belt-Eastern Venezuela Basin

A regional study has been performed on the heavy crude oils and bitumens from the Orinoco belt in the Eastern Venezuela Basin. The geochemical characterization of these hydrocarbons has been achieved using biological marker compounds including steranes, triterpanes, aromatic steroids and phenantrenes (GC-MS techniques) and petroporphyrins (analyzed by HPLC) as well as general parameters (S.A.R.A. composition, GC results, API gravity, etc.) determined in previous work. The heavy crudes oils and bitumens originated from early mature Cretaceous source rocks located at the North of the basin and are the result of severe biodegradation processes and accumulation in shallow reservoirs. Biodegradation shows different patterns according to the type of location (surface or subsurface). The classification of these hydrocarbons in terms of biodegradation was further complicated by the identification of mixed oils, which include most of the crude oils and bitumens in the Orinoco Belt with API gravities higher than 9-10 API. The crudes and bitumens from the Cerro Negro, Hamaca, and eastern Zuata areas seem to have been generated from the same source, while those of the Machete and western Zuata seem to have been generated from a different source rock. Furthermore, the Machete area oils and bitumens seem to be generatedmore » from source rocks at lower maturity stages.« less