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ESCANDON, LUIS, Lagoven S.A., Caracas, Venezuela

ABSTRACT: Petrophysical Evaluations of Sands in the Presence of Non-Radioactive Shale

In recent years, natural radioactivity of the rocks is been used as the best indicator for its shale content. This come be true only in absence of mica, feldspar and non-radioactive shales.

Micas and feldspar induce high radioactive levels that cannot be correlated with shaliness levels, and furthermore clean sandstones can be confused for shaly sands, silt and even for shales.

In the presence of non-radioactive shales, is the contrary, radioactivity tends to indicate very low levels. This characteristic

may show shaly or silty sands as clean sands with low resistivity. That could be erroneously interpreted as aquifers. If additional information is lacked so this interpretation is discarded.

Example for the Orinoco oil belt and from the lake Maracaibo Miocene are shown. Alternative techniques to estimate radioactivity.

Levels in presence of non-radioactive shales are also presented.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.