Geology and Petroleum Resources of Venezuela
H. Douglas Klemme
Venezuela occupies a peripheral position to the Guiana shield and craton in northern South America. The larger sedimentary basins of the Venezuelan craton zone are marginal cratonic basins (Lanos-Barinas), resulting from Tertiary Andean eastward movements, and basins formed by collisional, extensional, and transformed movement of the American portion of Tethys (eastern Venezuela-Trinidad). The smaller sedimentary basins of Venezuela are Tertiary transverse-wrench basins in the disturbed intermontane zone peripheral to the cratonic basins (Maracaibo, Falcon, parts of the Gulf of Venezuela, Carioca, and parts of Tobago-Margarita).
Venezuela accounts for 75% of the recoverable oil and 55% of the gas discovered in South America. These deposits occur primarily in two basins (East Venezuela and Maracaibo--where one complex, the Bolivar Coastal and Lake pools, represents 40% of South American discovered oil). The East Venezuela basin contains the Orinico heavy oil belt, currently assessed at 1 to 2 trillion bbl of oil in place. Source rocks for Venezuelan hydrocarbons are middle Cretaceous calcareous bituminous shales and marls (40% of discovered hydrocarbons), lower Tertiary deltaic and transitional shales, Paleocene-Eocene (40%), and Oligocene-Miocene deltaic and coastal shales (20%). A key factor in high recovery of hydrocarbons appears to be preservation of middle Cretaceous and lower Tertiary source rocks durin maturation and migration. Reservoirs are dominantly (> 90%) clastic sediments (sandstones) within, above, or updip from source sequences. Cap rocks are interbedded and overlying shale.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.