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Biomicrite, Marlstone, and Shale Properties. Exploration of Non–conventional Hydrocarbons from the Cretaceous Colombian Back–Arc Basin
Javier GUERRERO, Alejandra MEJÍA–MOLINA and José OSORNO
The non–conventional hydrocarbon potential of the Cretaceous Colombian back–arc basin is explored taking into consideration the properties of fine grained units, including biomicrite, marlstone, and shale, in terms of TOC contents, gas canisters, reflectance of vitrinite, porosity, permeability, pyrolysis, and organic geochemistry of samples collected from outcrop sections and wells of several localities in the core of the Eastern Cordillera, Middle Magdalena Valley (MMV), and Catatumbo. Best properties are from the Turonian to Santonian limestones of La Luna Formation and time–equivalent units, but other limestones of Albian and Campanian ages are prospective, including the Hilo Formation and the Oliní Group. La Luna Formation was deposited during a transgressive (TST) and relatively high sea level (HST) interval; it is composed of biomicrites of planktonic foraminifera, with minor inter–beddings of marlstones. Diagenetic cherts resulting from replacement of calcite by quartz are also present. The TOC average values of the formation are excellent, between 4.9% and 11.6% for sections in the area of Aguachica, 5.4% to 8.6% in the area of Barichara, and 6.1% to 7.2% in the area of Cúcuta. These high values of TOC are systematically associated with moderate values of thermal maturity, between 0.8% and 1.3% Ro; the interval contains mainly kerogen type II, with minor mixtures II–III.
Keywords: Cretaceous, back–arc, nonconventional hydrocarbons, limestones.