The oil seeps reported in this basin, as well as the petroleum discoveries (365 MBO) and gas (305 GCF) in 30 oil fields confirm the existence of at least one active petroleum system (Figure 2).
The petroleum systems proposed in the south zone are Caballos-Caballos (?), Caballos-Pepino (?), Villeta-Caballos (?), Villeta-Villeta (?) and Villeta-Pepino (?), and Macarena- Macarena (?) and Macarena-Pepino (?) in the north zone. Although the geochemical analyses are not yet conclusive, oil-rock correlation suggests two different migration pulses: i) Oligocene-Miocene, that would fill pre-Oligocene traps in the foothills and in the foreland area and, ii) Late Miocene-Pliocene whose filling should be associated to more recent structures in the foothills.
According to data collected at Uribe-1 well, the north zone rock-units prone to hydrocarbon generation, belong to the upper and middle intervals of the Macarena Group’s. At south, the Villeta and Caballos formations show very good characteristics as source rock. Cretaceous rocks, from Florencia sector also have good qualities for hydrocarbons generation.
In the southern portion of the basin, the quality of the source rocks increases westward, specially around the Orito field. The main geochemical characteristics of the Caguán and Putumayo source rocks are shown, as Van Krevelen diagrams, in (Figura 3).
The generation and migration model set out high possibilities of hydrocarbons trapping, as follows:
Caguán sector: The predominant crude migration pathways are:
Putumayo sector: Geochemical analysis of the oil found in source rocks offers little evidence to support a vertical migration, because oil traces do not exactly match with those extracts obtained from the source rock; therefore, crude may come from the west or from deeper yet undrilled areas.
According to the geochemical models, the crude migrated laterally from zones outside the basin’s current limit, in direction to the Eastern Cordillera. This hypothesis suggests an important expulsion process from Caballos and Villeta formations during Miocene – Early Pliocene at the south of the basin.
Cretaceous Caballos formation sandstones are the main basin reservoir, especially in the cases of faults - with displacements greater than 200 feet. Porosities of the Caballos sandstones vary from 10% to 16%; the average permeability is of about 50 millidarcies. Secondary reservoirs are found in sandstones interbedded in the Villeta formation and in conglomerates of the Pepino Formation.
Cretaceous Villeta shales and lutitic calcareous levels are excellent lateral and top seal units. Towards the foothills, thrust faults may act as effective seal mechanisms by putting in contact the Caballos Formation sandstones with fine grained sediments or igneous-metamorphic rocks.
The Rumiyaco and Orteguaza shales also constitute potential seals.
In the Putumayo area, the main traps are: folds associated to high angle reverse faults, anticlines related to thick skinned faults, anticlines related to reverse faults and back thrusts. For the Caguán zone, the trapping structures are related to folds formed by inversion of normal faults, as well as to folds generated by fault propagation mechanisms.
In the foreland area, the main traps are stratigraphic type, due to the onlapping of Cenozoic sequences above the economic basement.