The Sur Oriente block is located in the southeastern area of the Putumayo basin, near the town of Puerto Asis, and is one of Vetra's most important assets in Colombia. The block contains the Cohembí, Piñuña, Quillacinga, Curiquinga and Quinde fields. The Putumayo basin is underlain by the Precambrian crystalline igneous and metamorphic assemblage of the Guyana shield. The overlying sedimentary section thins eastwards on to this shield area. In the deeper parts of the basin up to 11,500 ft of Cretaceous and Tertiary are present. The main oil and gas reservoirs for the Putumayo basin in Colombia are in the Cretaceous Caballos and Villeta formations and the Tertiary Pepino formation. Putumayo Basin reservoirs for the Lower Cretaceous Caballo and Villeta U sandstones contain oils derived from a mixed marine and terrestrial source.