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Abstract

During 1983, the regional exploration and evaluation program of the 53,000 km2 (20,460 mi2) of the Orinoco Heavy Oil Belt was concluded. This evaluation, based on the interpretation of 25,000 km of seismic lines, 800 exploration wells, and 600 production tests, resulted in an estimation of 1.2 X 1012 barrels of oil in place. This confirms the existence in southeastern Venezuela of one of the largest oil accumulations in the world.

Production tests have shown great similarity with heavy-oil fields in traditional areas, i.e., average cold well rates between 100 and 800 b/d and a threefold increase of this figure upon steam soak.

The oil discovered has an average gravity of 9.5° API, with an average viscosity of 1500 cp at 99°C (210°F), sulfur content 3.6%, vanadium 420 ppm, and nickel 95 ppm.

One of the fundamental parts of the evaluation was the construction of sedimentary models to support the geological interpretation and the estimation of oil in place.

The stratigraphy of the area was established, permitting sedimentary models to be constructed, based on a well-to-well correlation and the analysis of 3290 m (10,800 ft) of conventional cores.

The main reservoir rocks are predominantly encountered in the basal section of the Tertiary and are formed of unconsolidated fluvio-deltaic sands.

Some oil has been trapped in rocks of Upper Cretaceous age, especially toward the west.

The trapping mechanism for oil in these conditions is mainly stratigraphic such as pinch-out and truncation of a complex set of meanders where intercutting of previously formed sand structures can occur. In some restricted areas, a combination of faulting and stratigraphy can be the trapping mechanism.

The physical and chemical properties of the oil are probably due to long-distance migration (some 100-150 km [60-90 mi]) and the consequent loss of volatiles and oxidation during migration.

Applying a recovery factor of 30% as a result of cyclic steam injection followed by steam drive, recoverable oil is estimated to be 245 X 109 bbl. Faja oil is basically naphthenic.

It is presently foreseen that production requirements from the Orinoco Heavy Oil Belt will be on the order of 500,000 bbl/day by the year 2000.

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