Венесуэльская предгорная впадина Маракайбо: геология и нефтеносность.

Foreland basin in Venezuela

The Maracaibo Basin, also known as Lake Maracaibo natural region, Lake Maracaibo depression or Lake Maracaibo Lowlands, is a foreland basin and one of the eight natural regions of Venezuela, found in the northwestern corner of Venezuela in South America. Covering over 36,657 square km, it is a hydrocarbon rich region that has produced over 30 billion bbl of oil with an estimated 44 billion bbl yet to be recovered. The basin is characterized by a large shallow tidal estuary, Lake Maracaibo, located near its center. The Maracaibo basin has a complex tectonic history that dates back to the Jurassic period with multiple evolution stages. Despite its complexity, these major tectonic stages are well preserved within its stratigraphy. This makes The Maracaibo basin one of the most valuable basins for reconstructing South America's early tectonic history.

The Maracaibo basin is surrounded by two mountain ranges, the Méridas Andes to the southeast and the Sierra de Perija to the west, with the Gulf of Venezuela to the north. The basin lies within a region of deformation created by the interactions of the Caribbean and South American plate boundaries. These interactions include the collision of the Caribbean plate with the South American plate in the Cenozoic era, which formed a belt of foreland basins across northern South America. There are three main fault zones associated with the basin: the Santa Marta Bucaramanga fault zone, the Boconó fault zone, and the Oca fault zone. These strike slip zones create a v shape around the basin which form a smaller plate known as the Maracaibo block. Within this v shaped wedge, multiple smaller fault zones are present including the Icotea strike slip fault. Thus the Maracaibo basin geometry is dominated by strike slip tectonics and subordinate folding with a main syncline, the Maracaibo syncline, striking north south through the center of Lake Maracaibo.

After rifting, the northern edge of the South American plate developed into a passive margin with the Proto Caribbean Seaway. This stable passive margin allowed for thermal subsidence to occur which began to increase due to the building up of the Cordillera Central range of Colombia. As plate migration proceeded, accretion along the South American plate increased. This accretion greatly influenced mountain building of the region. Uplift of the Sierra de Perijas occurred during the Oligocene whereas the Mérida Andes formed later in the middle Miocene. These sediments created the metasedimentary rocks of the La Quinta formation.

Oil was discovered in producible quantities in Venezuela in 1914 at the town of Mene Grande in the east central part of the Maracaibo basin near a surface oil seep. In December 1922, Royal Dutch Shell's George Reynolds (formerly with the Anglo Persian Oil Company) discovered the La Rosa Oil Field. The Barroso Well blew out at 100 thousand BOPD. In 1928, Jersey Standard discovered oil deposits under Lake Maracaibo. Today the basin accounts for approximately 50% of Venezuela's crude export capacity and approximately 15% of proven Venezuelan oil reserves. The region hosts one of the world's largest oil refinery complexes, the Paraguaná Refinery Complex. The nearby islands of Aruba and Curaçao also host large refineries that process oil from the Maracaibo basin. Together these refineries form the 'Venezuelan Circuit' of PDVSA. The Bolivar Coastal Field, BCF, on the eastern shore of Lake Maracaibo produces from Miocene sandstones and Eocene sandstones. West of Maracaibo, the La Paz Field produces from Cretaceous limestones, and oil is found in the stratigraphic traps of Boscan, Los Claros and the Urdaneta fields. Venezuela produces a mix of conventional heavy crude and unconventional crude derived from bitumen. This latter source, previously too expensive to produce in quantity, now makes up an increasing large percent of Venezuela's oil exports – 600,000 of Venezuela's three million barrels per day in 2006. In the Maracaibo Basin, the balance of reserves is toward its conventional deposits. As the country continues shifting toward bitumen production due to its increasing profitability and decreases in conventional reserves, the level of Maracaibo Basin oil production will decrease, while that of the Orinoco Belt and its massive bitumen deposits will increase.