Middle Magdalena Valley


Petroleum Geology

Hydrocarbon Evidences

After nearly a century of exploration in the basin, around 2412 MBO and 2.5 TCFG in 51 fields have been discovered. Among them is La Cira-Infantas, the first giant field discovered in Colombia.

Source Rock

In the Middle Magdalena Basin, the main source rocks were deposited during two global anoxic events and correspond to the limestones and shales of La Luna, Simití and Tablazo formations (Figure 2). Its kerogen is type II, TOC ranges from 1 and 6%; the vitrinite reflectance (Ro) varies from 1.1 to 1.2%.

Migration

A regional Eocene unconformity produces a system of migration pathways appropriate for the hydrocarbons transport. Three processes have been identified: 1) Direct vertical migration of hydrocarbon generated in La Luna Formation towards the Eocene unconformity. 2) Lateral migration along the Eocene sandstones. 3) Vertical migration through fault surfaces in areas where La Luna Formation is not in contact with the Eocene unconformity.

Reservoir Rock

97% of the proven oil in the basin comes from Cenozoic terrestrial sandstones (Lisama, Esmeraldas, La Paz, Colorado and Mugrosa formations), with an average of 15 to 20% porosity and permeability of 20 to 600 mD. Fractured limestones (Basal Calcareous Group and La Luna Formation) have a significant exploration potential; however, they have not been studied in detail.

Seal Rock

Marine shales of Simití and Umir formations represent the seal for potential Cretaceous reservoirs. In contrast, continental plastic claystones from Esmeraldas and Colorado formations are the seals for Cenozoic reservoirs.

Traps

Four major trap types have been identified: 1) Contractional fault-related folds hidden beneath thrust surfaces. 2) Thrust “duplex” structures with independent closure. 3) Fault-related closures 4) Footwall block traps below sealing faults (Figure 3).

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figure2 Figure 3