ORGANIC GEOCHEMISTRY AND ORIGIN OF THE HEAVY OILS IN THE EASTERN VENEZUELAN BASIN (HYDROUS-PYROLYSIS, ASPHALTENES, PETROLEUM, BIOMARTIERS)

The Eastern Venezuelan Basin, located in the central and eastern part of Venezuela, is considered to be a repository for one of the major oil deposits of the world. One section of the basin, the Orinoco Petroleum Belt (OPB), contains large deposits of heavy and superheavy oils reservoired in Oligocene-Miocene and Cretaceous strata. However, the origin of the heavy oils in the Orinoco Petroleum Belt has not yet been clearly ascertained. Computerized GC/MS studies of the distribution and relative abundance of biological markers (steranes and triterpanes) has established new evidence suggesting that both conventional and heavy oils from the OPB have originated from the same source rock. The results of gas-liquid chromatography, ('1)H and ('13)C NMR spectroscopy, infrared spectroscopy and elemental analysis indicate that heavy and superheavy oils from the OPB have been subjected to moderate thermal maturation as well as to different degrees of microbial alteration. Simulated microbial degradation of conventional (paraffinic-naphthenic) oils from the basin suggests that the heavy oils from the OPB are the result of microbial degradation.; Hydrous pyrolysis, a new method used for the first time in the study of asphaltenes from biodegraded oils, has led to the establishment of new criteria for oil-oil correlations. The hydrous pyrolysis results show that asphaltenes are potential generators of moderate quantities of materials similar to petroleum, containing n-paraffins, isoprenoids, steranes and triterpanes. Similarities among saturated hydrocarbon distributions were used to establish genetic associations among the biodegraded oils. Comparison of the distribution of the hydrocarbons in the pyrolyzates and conventional oils from the study area, indicates that a bulk of the heavy oils in the Orinoco Petroleum Belt (southern region of Anzoategui and Monagas states) may have originated from Cretaceous rocks.