Generation and Migration of Heavy Oils from Guarico and Southern Maturin Subbasins

Abstract

Results from an organic geochemical study from the western half of the Eastern Venezuela Basin (west of the Urica Fault) indicate that Cretaceous intervals from the Querecual and Tigre formations are the major source rocks for the naphtenic type oils. The Tertiary La Pascua, Merecure, and Lower Oficina intervals generated the paraphinic crudes. The mixture of naphtenic-paraphinic oils is interpreted to occur during migration or within the reservoirs. The thermal-maturity modeling from 56 wells, applied to the south of the Serrania del Interior frontal thrusts suggests that the active kitchens shifted gradually from the northwest to the southeast throughout the last 20 ma. To the north-northwest, the Cretaceous source rocks reached peak maturation and crudes were expelled prior to 15 ma. The Paleogene rocks reached similar conditions around 9 ma, and the Miocene intervals around 7 ma. The crudes generated between 15 and 18 ma migrated to the Orinoco Belt along unconformities and synthetic normal faults. Between 8 and 3 ma, the crudes followed a similar pathway, partially modified by the development of compactions faults. This later mechanism developed a series of antithetic faults which prevent the lateral migration and facilitate the vertical segregation. Oil in the Great Oficina areamore » was trapped during this time. Oil from the Anaco Trend was also trapped during this time associated with the inversion of a pre-Cretaceous half-graben.« less