Petroleum Systems and Reservoir Appraisal in the Sub-Andean Basins (Eastern Venezuela and Eastern Colombian Foothills)
François Roure, Nathalie Bordas-Lefloch, Jaime Toro, Charles Aubourg, Nicole Guilhaumou, Elisabeth Hernandez, Sophie Lecornec-Lance, Carlos Rivero, Philippe Robion, William Sassi, 2003. "Petroleum Systems and Reservoir Appraisal in the Sub-Andean Basins (Eastern Venezuela and Eastern Colombian Foothills)", The Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin Formation and Plate Tectonics, Claudio Bartolini, Richard T. Buffler, Jon F. Blickwede
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Major oil discoveries in the foothills of the Venezuelan and Colombian Andes have recently focused the interest of exploration companies toward sub-Andean basins. Seismic, well, and core data from the El Furrial (Venezuela) and Cusiana (Colombia) productive fields have been integrated herein with other regional information to document the evolution of the thrust belt and the history of the petroleum systems, and to propose practical guidelines for prediction of sandstone reservoir quality in such a complex geodynamic environment.
Although timing of deformation is slightly different in these areas of eastern Venezuela and Colombia, sedimentary and tectonic burial of the foreland autochthon in both regions led to the maturation of prolific Cretaceous marine source rocks, resulting in successive and diachronous hydrocarbon migration and trapping episodes.
Early sedimentary burial at the current location of the Serranía del Interior (Venezuela) and the Eastern Cordillera (Colombia) resulted in long-range migration of early-generated hydrocarbons toward the foreland, forming the large accumulation of hydrocarbon along the Faja Petrolifera (Eastern Venezuela). Early entrapped hydrocarbons also have been preserved in pre-Andean prospects of the Andean foothills, as evidenced by the complex charge history of the Cusiana field. However, wide areas of source rocks in the Andean foothills and adjacent foreland reached the oil window only during the late Neogene and Pliocene-Quaternary, when maximum burial was attained. This produced a second migration episode, coeval with the growth of frontal anticlinal prospects.
The main reservoir in Cusiana is fluvial sandstone of the Mirador Formation (Eocene); in El Furrial, it is sandstone of the Naricual-Merecure Formation (Oligocene). Pressure solution and quartz cementation decreased permeability of these sandstones. Results of studies of the anisotropy of the magnetic susceptibility (AMS), coupled with studies of fluid inclusions in quartz overgrowths and thermal modeling, demonstrate that sandstone reservoirs of these oil fields were compacted both vertically, by the load of the synflexural sequence, and horizontally, by tectonic stress (layer-parallel shortening) prior to being tectonically emplaced into the allochthon. Layer-parallel shortening by pressure solution is a major source of silica in the underthrust foreland.
Venezuelan and Colombian sandstones still have reasonably good reservoir characteristics, although they have been buried to great depths. Overpressure that developed in these reservoirs as a result of rapid foredeep sedimentation probably caused a delay in compaction. Early carbonate cements also may have contributed locally to prevent compaction until secondary porosity developed as a result of dissolution of this early diagenetic phase. Finally, development of structural closures and hydrocarbon trapping has resulted progressively in the shutting down of the hydraulic system, preventing the transport of exotic silica by regional fluid flow.
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The Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin Formation and Plate Tectonics
The Circum-Gulf of Mexico and the Caribbean has long been one of the world's most important petroleum provinces, as well as one of the world's most geologically complex regions. These two characteristics have resulted in an extensive amount of ongoing research by both industry and academia. AAPG Memoir 79, The Circum-Gulf of Mexico and the Caribbean, is the first volume in more than a decade to document such a wide range of research on the geology of this vast area. Of the total 44 papers, roughly two-thirds pertain to the Gulf of Mexico, with an emphasis on the Mexican portion of the basin, and to the petroliferous areas of the southern Caribbean, including Colombia, Venezuela, Cuba, and Trinidad and Tobago. The remaining papers relate to the Antilles and Central America, as well as a series of papers that address region-wide topics such as plate tectonic evolution. A significant number of papers were contributed by authors from national oil companies and universities from within the region.