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Detection of Tectonic and Subcompacted Geopressures in the Western Monagas-Anzoategui Overthrust Belt: A Structural Solution

REISTROFFER, JOHN, Corpoven S. A., Austin, TX

Abnormally high formation pressures have severely delayed exploration and development drilling in the Northern-Monagas-Anzoategui overthrust belt. The solution to these drilling problems lies in the successful prediction of tectonic and subcompacted geopressures. The study area is in Tacata field, located along the west edge of the Urica fault zone, at the southern compressive deformation front of the Northern-Monagas-Anzoategui overthrust belt in the Eastern Venezuela basin. Tag-11, a 17,800 ft wildcat well, was drilled in the Tacata field. Fifty-three (53) direct pressure measurements were taken in this well using wireline tools. The pressure measurements are combined with multiple log and biostratigraphic data to determine the nature of the over-pressures. Two types of over-pressur s are present: (1) tectonic and (2) tectonic + subcompaction.

Isolated pressure regimes are correlated to major thrust blocks on the seismic. A pressure transition zone is observed beneath an erosional unconformity, where eroded beds near the surface of an anticline are in hydraulic communication with the meteoric water table; beds close to the core, which have not been eroded, display abnormally high tectonic pressures. The proposed model identified the source of over-pressures and allows for the prediction of the top and base of each pressure regime.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)