In Apartadó-1 and Chigorodó-1 wells shales with source rock characteristics were drilled. Geochemical information of Necocli-1 well, drilled to the north of Urabá basin, on three samples tested, indicates the presence of Miocene source rocks. Although values of vitrinite reflectance (% Ro) point that these rocks are immature, the extrapolation of maturity data suggests that the rocks can reach oil generation window at a depth between 8500 and 9000 feet.
Sedimentary sequence drilled by the onshore Apartadó-1 and Chigorodó-1 wells, corresponds to a monotonous succession of sandstones intercalated locally with silty claystones. Siliciclastic rocks vary from quartzitic to lithic sandstones, fine grained to conglomeratic. ECOPETROL (1982) based on lithology criteria, electro-facies and seismic data, informally subdivided the sequence of these wells, in four units designated A, B, C and D (Figure 2). Sandstone levels of these units may eventually act as hydrocarbon reservoirs.
The sequence penetrated by wells Apartadó-1 and Chigorodó- 1 contains claystones intercalated with sandstones that would represent local seals to the accumulations.
Urabá Basin seismic data shows that the basement is regionally tilted toward northeast, creating by flexion space to accommodate sediment in that direction. The basement crops out towards the southwestern margin of the basin.
Low-displacement and variable vergence normal faults truncating sedimentary sequence against basement are interpreted from seismic lines. These structures form stratigraphic-structural traps, affecting the base of the stratigraphic sequence.
Shallowing of the basin to the southwest allows the wedging of younger rocks against basement. This geometry favors the presence of stratigraphic traps. The structural contours map shows the distribution of plays in the basin, according to the seismic interpretation (Figure 3). These plays correspond to geometries associated with wedging of sedimentary sequence against the basement (stratigraphic traps), especially towards the basin southwest margin and truncations against the basement by normal faulting (stratigraphicstructural traps).
In the offshore part of Urabá Basin, traps correspond to folds associated with inverse faults with stratigraphic control, wedging and potential coral growth developed against the basement structural slope.