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ABSTRACT

Oil accumulations in Trinidad were sourced by the Upper Cretaceous calcareous siliceous shales deposited along the Cretaceous passive margin of northern South America. Maturation of these source rocks, oil generation, migration and re-migration occurred in a foreland uplift-foredeep setting that resulted from interaction between Caribbean and South American plates during Lower Miocene to Recent times in the Trinidad area.

During Lower Miocene-Recent times, the foreland basin experienced strong compressional events, which controlled generation, migration, and accumulation of oil in Trinidad. A series of mature source rock kitchens formed in Lower Miocene-Recent times in the Southern and Columbus Basins southward of the Central Range Thrust which trends generally NE/SW. The thrusts and associated fractures first developed around 22 m.y.b.p. and served as near vertical migration paths for the oil generated in penecontemporaneous kitchens. This oil migrated into submarine fans deposited in the foredeep basin axis and older reservoirs deformed into structural traps. Further generation and migration of oil, and re-migration of earlier oil took place during Pliocene-Holocene times, when later thrusting and wrench faulting served as the migration paths. Extremely high sedimentation rates in Pliocene-Pleistocene time, concurrent with active faulting, was responsible for very rapid generation of oil and gas. Vertically migrating gas often mixed with earlier migrated oil in overlying reservoirs. This caused depletion of oil in light hydrocarbons with accompanied fractionation among hydrocarbon types resulting in heavier oil in lower reservoirs, and enrichment of light hydrocarbons and accumulation of gas-condensates in upper reservoirs. This process led to an oil-gravity stratification within about 10,000 feet of section.

These concepts enable prediction of petroleum occurrences onshore and offshore Trinidad.

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