Petroleum systems of the northwestern Tachira Depression, Venezuelan Andes

The tectonic evolution and sedimentation of the Tachira Depression was controlled by Paleozoic crustal scale discontinuities, partly or fully inverted during the pre-Andean (Paleocene) and Andean (Neogene) deformations. Outcrop samples were analyzed for source rock evaluation. La Luna, Los Cuervos and Carbonera formations are excellent potential oil sources. However, La Luna and Los Cuervos were the oil-generating units according to ID-modelling (BasinMod), defining La Luna-K/T(!) and Los Cuervos-K/T(!) systems. La Luna contains good to excellent oil prone kerogen type I-II, while Los Cuervos contains gas-oil prone type II-III. Oil seeps, expelled at the peak of oil generation stage (0.85-0.90 %R{sub o}), were derived from marine sources and genetically correlated to La Luna. No correlation of seeps with Los Cuervos was found. Although it exists to the southeast (Burgua depression). Potential clastic and carbonatic Cretaceous (K) and Tertiary (T) reservoirs and regional seals of the Colon and Leon Formations are widespread in the depression. Modelling results indicate that migration started during the Middle Miocene, related to the Andean tectonic loading. The subsequent migration took place northward, to be finally stopped against the Capacho and Bocono fault systems.