Geochemical modelling of the principal source rocks of the Barinas and Maracaibo basins, western Venezuela

This study presents a geochemical modelling of the principal source rocks in the western Venezuelan Basins. The area covers more than 100,000 km{sup 2}, and includes Lake Maracaibo and Barinas Basins. The geochemical modelling recognizes three source rocks: (1) A principal, K3-K4-K5 Cretaceous sequences, represented by La Luna, Capacho and Navay formations, (2) a secondary, corresponding to the T4 Oligocene sequence, represent by the Carbonera Formation, and (3) an accessory source rock, K7-K8 Paleocene sequences, represented by the carbonaceous shales and coals of the Orocue Group and Marcelina Formation. Three periods of hydrocarbon expulsion were defined for La Luna Formation (Early Eocene-Late Eocene, Middle Miocene-Early Miocene and Early Miocene-Holocene) and a principal period of hydrocarbon expulsion for Orocue Group and Carbonera Formation (Plio-Pleistocene and Middle Miocene Plio-Pleistocene). The 90% of hydrocarbons generated correspond to the principal source rock La Luna Formation, and the 10% to Tertiary source rocks (Carbonera Formation and Orocue Group). Five petroleum systems were identified: Lake Maracaibo, southwest of the Lake Maracaibo Basin, the Lara nappes, the extensive basins of eastern Zulia and the Barinas subbasin.