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Abstract: Petrophysical and Sedimentological Evaluation of the Tertiary Sandstones of Barua-Motatan, Eastern Zulia

Romulo Carmona, Selena Mederos

The combined application of conventional well logs such as resistivity, gamma ray, neutron density and sonic, and specialized logs such as acoustic image and analysis of fluid and rotary coring tool samples are excellent means of evaluating reservoir rock quality, fluid saturations, and hole conditions. This paper describes the application of such a technique and presents the results thereof of reservoir characterization as applied to an exploration well PAA-1X in the eastern coast of the Maracaibo Lake, Venezuela.

The PAA-1X well was drilled on the flank of a monocline west of Mene Grande fault near the border of Mene Grande field to explore the Misca Formation of Eocene age. Intermediate and Basal Pauji sandstones were not present in PAA-1X well, contrary to our expectations. The similarity of well logs and geological columns with an earlier exploration well, Tom-3X, confirmed this finding. The sandstones are medium to fine grained, with porosities of 5-21% and permeabilities of 0.02-0.8 md. The acoustic image log shows an ovalness of the hole, a characteristic typical of silty and shaly formations.

The interpretation with the aforementioned tools indicates that the exploratory well has very few thin productive intervals and is therefore likely to be deemed uneconomic. This is corroborated by the DST of the upper part of the Misoa Formation that produced only water. The study does indicate that this set of tools can be used very effectively in an integrated manner to accurately assess and evaluate prospects.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela