Los Cayos

Petroleum geology

Hydrocarbon Evidences

In Los Cayos basin, there is evidence of hydrocarbons which correspond to samples of oil (Gilsonite) and gas reported in the Miskito 1 and 2 wells (4250-5950 feet) in Middle Eocene calcarenites, shales and marls.

Source Rock

The bioclastic limestones found in Miskito wells are intercalated with calcareous shales, mudstones and micrites, which may act as hydrocarbon source rocks (Figure 2).

There is geochemical information from the Perlas-3 well, drilled in Nicaraguan platform, which indicates the existence of source facies in Early-Middle Eocene rocks, with good to excellent values of organic matter content (> 1.0%) and potential generation (S2) (> 2 mgHC /gr Rock).

According to maturity data (Tmax.), these rocks reach the oil generation window around 11 000 feet depth.

Reservoir Rock

Sedimentary sequence drilled by the Miskito - 1 and 2 wells shows the development of bioclastic facies (biocalcarenite, intracalcarenite and calcarenite) interbedded with calcareous shales, mudstones, micrites, and some levels of evaporites, suggesting its deposition in a low to moderate energy platform margin environment. In these wells not siliciclastic facies (sandstones and / or conglomerates) were found, which implies a distal position respect to the source areas of terrigenous material.

This situation indicates that the units that could act as reservoirs would correspond to levels of middle Eocene to Miocene bioclastic limestones in Miskitos wells; diagenetic and mechanical effects may increase secondary porosity of these rocks.

Seal Rock

Calcareous shales, mudstones, micrites and evaporites drilled in Miskitos wells, may act as seals for hydrocarbon accumulations. Its thickness ranges from 10 to 200 feet. In the synclines limited by basement highs is possible the existence of deep marine shales acting as source and seal rocks for hydrocarbons, considering its location on the slope of the Nicaraguan platform.


Los Cayos Basin seismic and bathymetric information indicates a tectonic blocks structural style, in which volcanic highs are the islands and cays, and low blocks form depocenters with thick sedimentary sequences of up to 3 seconds in seismic profiles (Figure 3).

In some of the structural high as in the area of the Miskitos wells, limestone deposits in reefs structures and atolls with little burial can be seen as an opportunity for biogenic gas exploration, similar to the Chuchupa and Ballena fields in the Guajira area.

Structurally low areas with the sedimentary sequence possibly formed in turbidite environments, may be favorable for thermogenic gas generation. Towards the synclines flanks in the onlap terminations of these sedimentary sequences, favorable conditions can be present for hydrocarbon accumulation in structural-stratigraphic traps.

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