Regional tectonics, sequence stratigraphy and reservoir properties of Eocene clastic sedimentation, Maracaibo Basin, Venezuela



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The Maracaibo basin of Venezuela is one of the most prolific hydrocarbon basins in the world. During the Paleogene, oblique collision between the Caribbean and South American plates produced a 4-km-thick wedge of clastic sediments, where over 40 billion barrels of hydrocarbons have been produced. Previous studies in the Eocene interval are focused either at a large regional scale or a field-size reservoir scale. Integration between both scales of observation has not been previously done, and, as a consequence, the effect of regional tectonics is not considered in the small-scale stratigraphic record. The aim of this dissertation is to study the interplay of tectonic and stratigraphic variables that controlled the Eocene sedimentation in the Maracaibo basin, and to establish a geologic model that incorporates data from a regional to reservoir scale. Interpretation of 2-D and 3-D seismic data in the central and eastern Maracaibo basin reveals two major tectonic features formed during Paleogene collision between the Caribbean and the South American plates: 1) a late Paleocene-early Eocene foreland basin; and 2) a middle-late Eocene lateral ramp fault. The lateral ramp fault forms a paleogeographic facies boundary separating a less faulted and folded shelf area to the west from a fold-thrust belt to the east. In the Eocene Maracaibo shelf area, intraplate deformation occurs by NNE-striking left-lateral faulting with pull-apart basins localized at fault stepovers. Three-dimensional seismic time slice interpretation of more than 2000 km² of 3-D seismic data allows mapping of the Icotea pull-apart basin. Extension of the Icotea pull-apart basin is localized on pre-existing NW-SE-striking normal faults, formed by Paleocene-Eocene plate flexure during the foreland basin period. Detailed sequence stratigraphic interpretation of the central Maracaibo basin was carried out using 330 wells and 3-D visualization methods that combined well and 3-D seismic data techniques providing greater vertical and lateral resolution (pseudo-seismic). These data reveal that Eocene clastic sedimentation is controlled by tectonic subsidence and to a lesser degree by changes in sediment supply and eustasy. Hydrocarbon reservoirs of the central Maracaibo basin are concentrated in distributary channels and tidal sand bar facies on structural highs produced by strike-slip motion of N-NE-striking faults. Depositional environments and fluid content of Eocene reservoirs are inferred from cross sections based on closely spaced well logs.