An overview of the petroleum system of Maracaibo Basin

Abstract

The geologically complex Maracaibo Basin in northwestern Venezuela is one of the most prolific hydrocarbon basins in the world. Having a basinal area of 50,000 km2 (19,300 mi2), the basin has produced more than 30 billion bbl of oil, with estimated recoverable oil reserves of more than 44 billion bbl. The central elements of the petroleum system of the basin include (1) a world-class source rock (Upper Cretaceous La Luna Formation), deposited on a shelf-to-slope environment under anoxic conditions and modified by intermittent oxygenated periods and tectonic events; (2) high-quality clastic reservoir rocks deposited in Eocene and Miocene fluviodeltaic settings; (3) two main periods of rapid tectonic subsidence responsible for two pulses of voluminous hydrocarbon generation, first, during Paleogene Caribbean–South American oblique plate collision and, second, during the Neogene uplift of the Sierra de Perij–Mrida Andes; and (4) lateral and vertical migration of oil along strike-slip, normal, and inverted faults, as well as a regional unconformity of late Eocene–Oligocene age. The maturation, migration, and trapping of hydrocarbons were closely controlled by the tectonic evolution of the Maracaibo Basin. During the Paleogene, the development of a foredeep along the northeastern margin of the basin and the strike-slip reactivation of the rift-related Jurassic faults on the Maracaibo platform controlled the early structural setting of the source and reservoir rocks. Hydrocarbons migrated updip from source rocks beneath the north-northeastern margin of the basin along north-south strike-slip faults and into overlying Eocene clastic reservoirs in the south-central parts of the basin. The second period of the Maracaibo Basin petroleum system developed during subaerial exposure of most of the Maracaibo Basin during Oligocene–Miocene uplift of the adjacent Sierra de Perij and Mrida Andes. Uplift of mountain ranges surrounding the basin folded and depressed the interior of the basin to form the extensive Maracaibo syncline. Because of the formation of the Maracaibo syncline, oil generation began in the central and southern parts of the synclinal basin and migrated northward. Hydrocarbons migrated up the flanks of the Maracaibo syncline along reactivated strike-slip faults and into Miocene rocks adjacent to the uplifted mountain ranges. Escaping oil has formed numerous surface seeps along the edges of the Maracaibo Basin.