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Stratification of Oils in Columbus Basin, Offshore Trinidad

L. M. Ross, R. L. Ames

Over 100 oils were collected in 1981 from wellheads in Amoco Trinidad's Teak, Samaan, and Poui fields. As these fields have been the subject of many geologic and engineering studies, we have an excellent laboratory to investigate the effects of both lateral and vertical migration on crude oil composition. It is apparent from this study that the oil composition in these complexly faulted Pliocene-Pleistocene reservoirs is strongly controlled by vertical migration.

All of the oils from these fields are assumed to belong to one genetic oil type and from previous drilling no mature oil-source sequence has been encountered. Therefore, variations in the molecular composition of the oils should be related to either migration effects or subsurface alteration processes (thermal maturation or bacterial degradation).

The results of the study indicate that all three fields exhibit dynamic oil migration systems. Oils in Samaan field reflect a vertical stratification pattern with waxy oils in the deepest sands and light oils in the shallowest sands. Even though Samaan oils generally evidence less diversity than that found in Teak and Poui fields, all three fields demonstrate similar oil stratification patterns.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.