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Twenty-five crude oils from the Ghadames basin, western Libya, were analyzed to distinguish genetically distinct oil families and to attempt identification of different geologic processes that have affected the oils. The oils came from reservoirs ranging in age from Cambrian to Triassic. The samples were analyzed by mass spectrometry to identify molecular types of compounds present and to determine the stable carbon isotope values for the heavy saturate and heavy aromatic fractions. Gas chromatography was used to analyze the light gasoline fractions and the heavy saturate fractions of the oils.
Significant differences were noted between oils from different parts of the basin. At least 4 different Paleozoic oil families were distinguished. The oils from Triassic reservoirs appear to have migrated from Paleozoic strata. Alteration of some of the oils by water flushing and by bacterial degradation is evident. A study of the hydrodynamic flow of formation waters in the major reservoir zones supports the chemical evidence that flushing has affected the compositions of some of the oils.
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