EXPLORATION AND EVALUATION OF THE ZUATA AREA, ORINOCO OIL BELT, VENEZUELA

Exploration activity in the Zuata area within the Orinoco Oil Belt in Venezuela has included the drilling of 161 wells and the recording of 3,000 km of seismic lines. Based on these results, a productive area of 9,200 sq. km has been defined, containing 79.3 B cu.m. (499 B brl)? of crude oil in-place, with densities ranging from 1.021 to 0.934 g/cu.cm (7–20 °API). The principal productive sands are of the Tertiary Officina Formation, deposited during a transgression which occurred in the Miocene. A distinctive feature of the productive formation is its progressive onlap against older rocks (Cretaceous, Paleozoic or Pre-Cambrian) in a southerly direction which, together with overlying shales, provide the trapping mechanism for the oil which migrated from the north. The productive sands were deposited in a fluvial to coastal plain with deltaic developments. The sands are unconsolidated and fine- to very coarse-grained, with an average porosity of 34% and a permeability of 7μm²(7D). The structure is a monocline dipping 0.5° to 2° to the NE, and the trapping mechanism is principally stratigraphic. In the 134 producers, 300 tests were completed which resulted in an average production of 25 cu.m/d (160 b/d) per well by beam pumping without dilution or heat. Subsequently, a steam cycle of 5,000 metric tons was injected into 16 wells; production increased to some 200 cu.m/d (1,250 b/d) per well. For future development, a Priority Area has been selected: this Area covers 3,500 sq kin, and contains 40.5 B cu.m (255 B brl) of crude oil with a density range of 1.014 to 0.993 g/cu.cm (8–11°API). The oil is at an average depth of 610 m, and the average net oil-sand thickness is 60 m. The oil-sand is generally divided into three zones separated by shales, and the gross productive thickness is some 110 m. Similar to Maraven ‘s experience in the oilfields of the Bolivar Coast in Western Venezuela, it may be expected that reservoir compaction will occur, and will be efficiently activated by steam-soak or “huff and puff’. Based on core compressibility measurements, a recovery factor from compaction drive and solution gas treatments could reach 12 % of the oil in-place. Under this premise, the Priority Area could have a potential recovery of 4.9 B cu. m. (30.6 B brl), which could support a production of 160,000 cu.m/d(1MM b/d) for 100 years. Any follow-up steam drive can be assumed to recover at least an additional 10% of the oil in-place. A Conceptual Development Plan based on clusters, inclined wells (due to the shallow depth) and steam soak has been proposed, and will be validated by a pilot test consisting of a seven-well cluster.