Abstract

GROSSO, Santiago; LOPEZ, Ramiro; VERGANI, Gustavo  and  O'LEARY, Sol. Natural fractured carbonate reservoirs in Caimancito field (Yacoraite Formation), cretaceous basin of northwestern Argentina. Rev. Asoc. Geol. Argent. [online]. 2013, vol.70, n.1, pp.53-69. ISSN 0004-4822.

The Yacoraite Formation lithology is mainly composed by carbonate rocks of gray whitish-yellowish colors and also by marls, siltstones, sandstones and claystones of middle gray, pale green or reddish-purple color. The interbeded black claystones are the hydrocarbon source rock and the carbonates are the reservoir. It is deposited in the Cretaceous/Tertiary basin of the northwestern Argentina inside the Balbuena Subgroup which involves also the underlying Lecho Formation originated during an episode of thermal subsidence. A previously rifting period occured and was deposited the Pirgua Subgroup. Both subgroups are the base of Salta Group (Neocomian-Eocene). The Caimancito oil field is located east of Calilegua hills, in sub-Andean foothill, at the Jujuy province, Argentina. The main reservoir is composed by fractured dolomites and limestones of the Yacoraite Formation with an average porosity of 5.7 % and permeability from 0.1 mD to 8.1 mD and some values up to 250 mD. The fractures observed in borehole images and dip-meter are high dipping angle with three different main trends: E-W and NW-SE (Type I) interpreted as open and N-S (Type II) as closed. The sets fracture intersections produce rectangular blocks varying in size according to the lithology and stratigraphy. The fractures tend to be located in carbonates rather than in silicicoclastics. The fracture intensity increases as the bed thinning. The trends of the reverse faults are N-S parallel to the Andean hills and the normal faults are E-W trend.

Keywords : Fractured reservoir; Carbonates; Hydrocarbons; Yacoraite Formation.

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