2-D Modeling of Generation, Migration, Oil Mixture and Biodegradation in Ceuta, South-East of the Maracaibo Basin: ABSTRACT

Abstract

Oil in the Ceuta area have been found in Cretaceous and Tertiary reservoirs. A recent 300 sq km 3-D survey has confirmed the existence of strong faulting that determined important thickness variations of deltaic Eocene prograding sediments between the eastern and western areas. A major sequence boundary is associated to uplifting and erosion from the upper Eocene to the lower Miocene, inversion playing an important role in hydrocarbon entrapment, at the same time that a progressive tilting towards the southeast developed, controlling most of the migration directions. Added to the differences in burial histories, a variable heat flow field is estimated through the area, considering that changes in thicknesses and lithologies convey a significant part in the bulk thermal conductivities of the rock column. Oil-source rock correlation based on biomarker fingerprints relates the existing crude to the Cretaceous La Luna source rock. Rock maturity measurements constrain the thermal evolution model and we conclude that expulsion of oil in the east occurred during the Eocene, while in the east is during the upper Miocene. The identification by biological markers of crudes of different maturities validate the hypothesis of drainage areas of different geological and thermal evolution together with complex migration paths. more » As a result of exposure of crudes to biodegradation during Eocene times, a loss of an extensive volume of hydrocarbons is believed to have occurred. The former existence of this oil is recorded by the presence of demetilated hopanes, indicative of a high level of biodegradation, mixed with unaltered oils. All these processes have been examined by computerized 2-D modeling. « less