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Tectonic and Stratigraphic Controls on the Orinoco Heavy Oil Belt, Eastern Venezuela Foreland Basin

Hugo A. Castellanos1, Alejandro Escalona2, Luis Rodriguez3, and Paul Mann2
1 The University of Texas at Austin, Austin, TX
2 Jackson School of Geosciences, The University of Texas at Austin, Austin, TX
3 Orifuels Sinoven, S.A, Puerto La Cruz, Venezuela

The Orinoco heavy oil belt, located in eastern Venezuela, is the second largest hydrocarbon accumulation of the world after the western Canada heavy oil and tar deposit of 1700 BBOE. With at least 1200 BBOE of 8°-10° API oil in place, the Orinoco heavy oil belt is now the focus of intensive study to better understand the subsurface geology in order to improve recovery of its shallow (<1 km) heavy oil deposits. The Orinoco heavy oil belt represents the distal southern edge of the late Oligocene-Miocene Eastern Venezuela foreland basin that was formed during oblique Caribbean-South American plate convergence. Tectonic loading along the Eastern Venezuela foredeep produced a forebulge beneath the present-day heavy oil belt. South-southeast migration of the forebulge occurred as a result of Oligocene-Miocene oblique convergence to the north and created an asymmetrical, down-to-the-north accommodation space. Accommodation space at the southern edge of the foreland basin was increased by down-to-the-north normal faults formed as a response to regional basinal flexure. We use 2D seismic lines and wells to document a series of west-to-east migrating and backstepping fluvio-deltaic systems related to the eastward flowing Orinoco river system and smaller rivers emanating from the Guayana shield. These terrigenous point sources filled the accommodation space with high-quality reservoir sands starting in early Oligocene time and extending through the Plio-Pleistocene. Maturation of Late Cretaceous marine source rocks started ~12 Ma and petroleum migrated updip into the shallow Orinoco Oil Belt reservoirs where oils were subsequently heavily biodegraded.