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.
Figures & Tables
Exploration for Heavy Crude Oil and Natural Bitumen
Gross volumes of oil, which must be kept in mind to address the volume/size framework, may be thought of in order from largest to probably smallest volumes as follows: (1) generated; (2) dissipated; (3) degraded/ partially preserved; and (4) trapped and conventionally producible. Basic knowledge of these volumes may be from greatest to least in essentially reverse order.
The 332 largest known accumulations (less than 1% of the total number) account for more than three-quarters of the known 7.6 trillion bbl of oil and heavy oil or tar in more than 40,000 accumulations in the world. About 2.4 trillion bbl of estimated undiscovered conventional oil added to the known volume of 7.6 trillion bbl yields a total of 10 trillion bbl known or reasonably estimated. World-wide cumulative production of about 500 billion bbl of oil accounts for only 5% of the gross.
Oil in place must be estimated for conventional oil fields before comparison with heavy oil and tar accumulations. The size range of accumulations considered in the size distribution of the 332 largest known accumulations is from 0.8 to 1850 billion bbl of oil. The smallest conventional fields in the distribution are about 1 billion bbl because the size cut-off is 0.5 billion bbl of oil recoverable. The size distribution of the 332 largest known accumulations approaches log normal and is overwhelmed by the largest three supergiant tar deposits that hold nearly half of the total 5495 billion bbl.
Globally, the largest three accumulations, all heavy oil or tar, are in South and North America; the two largest conventional oil fields are in the Middle East. Prudhoe Bay and East Texas fields rank 18 and 34, respectively, in descending size order.