Abstract

ROSSELLO, Eduardo A.  and  GARCIA-SANCHEZ, Rolando. NON-CONVENTIONAL TRAPS ASSOCIATED WITH OPHIOLITES OF THE NORTHERN HYDROCARBON BELT (HAVANA-MATANZAS, CUBA). bol.geol. [online]. 2017, vol.39, n.3, pp.41-54. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v39n3-2017003.

The geological characteristics of the Cuban territory are the result of a multi-episodic tectosedimentary history, represented by a series of sequences and structures closely related to the evolution of the Western Caribbean. Mafic and ultramafic rocks, mainly serpentinized peridotites, gabbros and basalts, are distributed throughout the northern margin of Cuba (~ 200 km of exposure) and are mostly associated with ophiolitic complexes linked to the evolution of the Carribean plate. The northern hydrocarbon belt comprises oceanic volcano-sedimentary sequences forming a stack of thrust sheets (ophiolites-Mesozoic sedimentary carbonates); such configuration is the responsible for the reservoir and seal conditions of the many hydrocarbon fields in the area. Oil accumulations occur mainly at depths around 500 to 800 m, locally up to 3,000 m, with oil-saturated thicknesses up to 400 m and 9º to 19º API. Reservoirs are mainly fractured serpentinites, with mean log porosity values of ~ 6% (and up to 8% SWC) with permeabilities varying between 0.001 to 21.4 mD. Porous to dual porous-fractured reservoirs occur in other fields as tectonic slabs of cataclastic serpentinites, peridotites, gabbros and diabases, with porosities < 3% (in log) and up to 9% (SWC) and permeabilities ranging between 0.001 - 290 mD (7,400 mD average). The highest porosities in the area are recorded in fractured and weathered peridotites and grabbros, with log-derived porosity values up to 11% (4% average) and sidewall core up to 8%. Good quality seals are locally formed by the weathering of serpentinites. New concepts in oil exploration involve the analysis of ophiolitic complexes and related rocks in the Pacific margin as potential promising targets. Thus, the resemblance of these Cuban ophiolitic complexes with their under-explored South American analogs opens a new opportunity for hydrocarbon exploration in the offshore of Colombia, Peru and Chile.

Keywords : Non-conventional reservoirs; hydrocarbons; structural traps; ophiolites; Cuba.

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