t:- The Orinoco Heavy Oil Belt (Venezuela) has 460 km long and between 40 and 80 km wide, with a total area of 55,300 km2, containing the biggest extra-heavy oil reserves in the world. Within this belt, the Miocene Oficina Formation in the Petrocedeño field, Junín area, has been producing extra-heavy oil (8.5° API) for more than 20 years. The field development has generated a detailed picture of its structural, sedimentological and stratigraphic setting, along with an excellent understanding of its static/dynamic properties. Reservoir zonation was successfully applied based on a 3rd-order sequence stratigraphic framework for which a detailed sedimentological understanding was crucial. In the study area, Lower Oficina Formation (Morichal Member) is characterized by a fluvial dominated system at the base, to a tide-dominated lower delta plain and subsequently a tide-dominated, subtidal, upper deltaic-platform to the top. The current sequence stratigraphic model cannot explain the presence of anomalous thick channelized sandstones with an apparent erratic distribution in the upper part of the interpreted transgressive system tract. The detailed study of the C1 parasequence set, allowed the identification of a sequence boundary not recognized in previous models. This sequence boundary was the result of a relative sea level fall, creating an incised valley system. These incised valleys show great complexity and sinuosity, creating a very narrow and localized network in the study area. 3D seismic, a dense network of wells (vertical, inclined and horizontal) and a number of cores, allowed the construction of high-resolution model to enable the optimization of cold production in this area

Keywords : Orinoco Heavy Oil Belt; Oficina Formation; Sequence Stratigraphy; Venezuela