--> Use of Deep Aquifers in the Zuata Area, Orinoco Tar Belt, by J. L. Perez; #90986 (1994).

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Abstract: Use of Deep Aquifers in the Zuata Area, Orinoco Tar Belt

Jose L. Perez

The Orinoco Tar Belt, located beneath the plains north of the Orinoco river, with an estimated oil in place volume of 1.2 × 1012 barrels is the biggest heavy/extra-heavy/oil/bitumen accumulation in the world. The Zuata area holds about 40% of these resources (500 × 109 barrels). Currently, two projects, aiming at a combined sustained production of 240,000 BOPD during a period of 35 years, are undergoing a phase of basic engineering design.

Under the selected production method, cyclic steam injection, a vast amount of water will be needed, particularly for steam generation. Since a large portion of this steam returns back to the surface, as water mixed with the produced oil, the project design should allow for alternatives for both supply and disposal of water.

Original plans asked for the construction of a water treatment facility at a lateral lagoon of the Orinoco river. From there, the water would be pumped through a pipeline (+/-70 km) to the production areas. For disposal purposes, an evaporation pool of some 16 hectares (400 × 400 m) would be needed in order to treat the effluents of the project. Besides the high cost, the environmental risk associated with the construction of these facilities could be an influential factor on the project design.

After a geological appraisal of the stratigraphic column present in the Zuata area, it was found that the unconsolidated sands of the Tigre Formation, Cretaceous in age, could constitute an optimal recipient for the effluents of the project. These water-bearing beds are widely distributed across the Zuata area and have a porosity, derived from electric logs, of around 30%. Furthermore, their position, underlaying and separated from the oil producing sands of the Oficina Formation, make them a sealed container far apart from the shallower and fresher aquifers.

Electric logs from wells drilled in the area show an interval of water bearing sands situated in the middle and upper Oficina Formation. These beds are rather persistent over the area, and although no water samples have been recovered, log characteristics suggest these aquifers to be of rather low salinity. A series of tests are planned to appraise them in the near future. Their depth make them unsuitable for farming purposes. However, they represent an affordable target for oil related activities in the Zuata area.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994