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Chapter 17: Petroleum Potential of Permian Carbonates in Northern South America
In the last decade, Paleozoic rocks have been recognized as having potential for future resources of oil and gas in several countries around the world. The petroleum potential of the upper Paleozoic strata in northern South America is noteworthy in view of the correlations with hydrocarbon-bearing strata and source rocks in neighboring Brazil and Peru–Bolivia, and the southern United States, for both conventional and unconventional oil and gas reservoirs. In the northern part of South America, specifically in Venezuela and Colombia, the upper Paleozoic stratigraphic record is poorly documented and understood, but the succession there reveals major changes in facies, which can be related to global-scale events. These changes have been described through detailed fieldwork in the Venezuelan Andes, supported by petrographic and geochemical studies. This dataset forms the basis for the interpretation of the potential petroleum systems in this area, along with the available published information. Sedimentation during the Permian occurred on an extensive ramp, which dipped basinward, probably toward the north, toward the open ocean within the foreland basin, which has been named the Mucuchachi Basin (MB). The Permian rocks in the MB extend through Colombia to the west and southwest, where a few sections of limestone and shale with fusulinids occur. The MB may well have been connected to the basins in Peru and Bolivia to the southwest and with those in the Mexican and Guatemala areas to the north, where a similar stratigraphic succession is developed. Elements of the petroleum system for these Permian rocks include the presence of source rocks since values of total organic carbon reach 5% in some shales. However, indicators of thermal maturity suggest an over-mature level. On the other hand, a thermal simulation derived from basin modeling software and clumped isotopes thermometry suggests that strata could have been in the oil and gas window during the Cenozoic. Thus there is the likelihood of hydrocarbons having been expelled upward into stratigraphically younger reservoirs, where fractured fine-grained clastic facies and sandstone horizons could have the potential to provide reservoir rocks. The presence of fine-grained facies with low permeability suggests that these Permian rocks could have the potential to provide a sealing capacity as well as the possibility of being part of stratigraphic traps. In addition, several authors have pointed out potential structural traps in the Barinas–Apure Basin and these could have extended to the western areas of the Los Llanos Basin in Colombia are restricted to the Tachira Graben.
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