Sinú-San Jacinto- Lower Magdalena Valley


Petroleum geology

Hydrocarbon Evidences

There are a lot of evidences of oil in the Sinú-San Jacinto- Lower Magdalena Valley area, especially in areas of Sinú and San Jacinto Folded belt, where have been reported over a hundred oil and gas seeps.

Source Rock

In the Lower Magdalena Valley, Ciénaga de Oro formation has interbedded shales of marine transitional origin that act as source rocks, according to geochemical available data. In Sinú and San Jacinto fold belts; there are thick sequences of marine Cenozoic shales (Maralú, Chengue and Carmen formations), which according to geochemical data can act as source rocks and seals to the reservoirs and their accumulations. Underlying the whole sequence lies Late Cretaceous age Cansona Formation, composed primarily of marine shales, which is also a potential source rock (Figure 2).

Migration

At Sinú-San Jacinto Basin migration of hydrocarbons along fractures is documented by the abundant oil and gas seeps. For the Lower Magdalena Valley, active source rock areas for generation / expulsion phases are presented in the so-called Plato sub-basin; between Guamito - 1 to the northeast and Pijiño-1 wells to the south. Oil API gravity in the basin ranges from 30° to 52°. The sulfur content is very low, while the concentration of paraffin is relatively high. Several geochemical parameters indicate that most oil has been generated in a proximal siliciclastic environment. Four different migration patterns have been proposed: 1) Cicuco-Boquete area. 2) Momposina Area. 3) Güepaje Area and 4) Apure Region. Much of the migration has happened along the fractures network and fault planes.

Reservoir Rock

The reservoir rocks in the Lower Magdalena Valley correspond to a thick sandstones sequence of fluvial to deltaic origin of the Ciénaga de Oro Formation. At San Jacinto Folded Belt, the main reservoir rocks are the Cenozoic sandstones of marine-deltaic origin from San Jacinto, Maco and San Cayetano formations. Locally, fractured limestones from La Risa and Toluviejo formations may be potential additional reservoirs. At Sinú Folded Belt, the main reservoir rocks are the Cenozoic sandstones of marine- deltaic origin from Paujil, Floresanto, Pavo and Maco formations. Locally, fractured limestones of La Risa Formation may be potential additional reservoirs. In Urabá Basin offshore zone, the objective as a reservoir could be coralline limestones given the favorable reservoir conditions observed in the province, a bay with freshwater downloads and moderate sedimentation rates.

Seal Rock

In the Lower Magdalena Valley, Ciénaga de Oro Formation has interbedded shales of fluvial to marine transitional origin acting as local seals. In the case of Sinú and San Jacinto fold belts, Cenozoic marine shales of Maralú, Chengue and Carmen formations, may act as seals to the reservoirs and their accumulations.

Traps

In the Lower Magdalena Valley, traps corresponds to compresional folds related to Romeral fault system, reservoir truncations by faulting associated with compressive and extensive events in the basin, reservoir onlapping against basement and basement highs in which calcareous facies or coarse siliciclastic are developed. At San Jacinto Folded Belt, traps correspond to compresional folds Related to Romeral fault system of varying lengths between 2 and 30 km according to surface mapping, reservoir truncations by faulting associated with compression episodes in the Folded Belt and locally channels fills in incision valleys. At Sinú Folded Belt, traps correspond to folds associated with early stages of diapirs formation that do not disrupt completely the sequence. A favorable aspect of this type of folding is that according to surface geology are tight but laterally extensive, with lengths between 5 and 20 km, reservoir truncations against the diapirs, and truncation by sindepositional unconformities caused by the deformation associated with mud diapirs vertical displacement (Figure 3).

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