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Abstract

The Cedro area paleocanyon constitutes a large tectonic-erosional feature with an area of approximately 400 sq km (154 sq mi) in the Espirito Santo Basin on the east coast of central Brazil. Early faulting triggered erosional activity in Lower Cretaceous time, resulting in the formation of a large trough which was then filled with clastic sediments of Upper Cretaceous age.

A second erosional cycle at the end of the Cretaceous period created a second, younger canyon which was subsequently filled with terrigenous Tertiary sediments.

The tectonic activity which controlled this occurrence was rifting associated with the separation of the South American and African continents, renewed at the end of the Lower Cretaceous.

Conventional seismic data and wells drilled in the area show the predominantly argillaceous sedimentation which filled the canyon to onlap against the canyon walls with interfingered sandy lenses. These lenses, now identified as turbidite deposits, have their major expression in the Cretaceous section. The Tertiary Paleocene section has less well-developed reservoirs, but both sequences produce hydrocarbons from stratigraphic traps. The sedimentary section which filled the canyon is termed the Urucutuca formation. Identification of individual productive members by means of conventional seismic data is highly problematical due to the limits of resolution of the data.

Inversion of seismic traces to generate synthetic sonic logs permits the identification and definition of members or bodies of interest, and their lateral extension, due to differences in seismic velocity between these and the surrounding shales. The lateral extension of these bodies is usually limited.

Stratigraphic interpretation can be used to separate the main depositional sequences. The method can also be used to identify the most favorable sites for the accumulation of sandstones.

Wells drilled after the inversion processing in the south part of the paleocanyon have shown good correlation between the geophysical predictions and the geological conditions found.

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