Abstract: Thermal History and Timing of Hydrocarbon Expulsion in the Maracaibo Basin, Venezuela

Christopher White, Luis Mompart

The aim of this paper is to contribute towards the understanding of the thermal history of La Luna and Orocui source rocks and their related hydrocarbon generation and expulsion in the Maracaibo basin. The paper is derived from an integrated geochemical model obtained during a recent multidisciplinary regional study. Among data compiled or interpreted are geothermal gradients which increase in value towards the northeast and southwest, with a minimum in the west coast of the lake and local maxima along NNE-SSW structural alignments; heat flow value which reflect this same pattern; eroded Eocene sediment thicknesses of up to 1500 ft in the lake area which contrast with 10,000 ft used in previous studies. These data, together with vitrinite reflectance and T_max m turity values, well and seismic isopachs of Cretaceous and Tertiary stratigraphic sequences, were modelled using BasinMod TM, a basin modelling software. Highlights of this are time of expulsion maps that illustrate how the first expulsion of hydrocarbons from La Luna occurred in the northeastern area of the Basin during Early (not Middle) Eocene times. The oil expulsion window migrated towards the southwest and eventually the northwest, but bypassing the western coast of the lake, presently immature (contrary to previous work), and gas expulsion is occurring now in the Miocene trough northwest of the Andes Mountains. The thermal history of the Paleogene source rocks (Orocui Group and Misoa Formation), shows generation/expulsion mainly in the southwest of the Basin, since Late Miocene.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela