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Abstract: Application of Azimuthal Resistivity Images to Identify Pay Zones in Highly Shale Laminated Sands of the Upper C Eocene Reservoir of Ceuta Field in Lake Maracaibo, Venezuela

Marco Vivas, Ovidio Suarez

The objective of this work is to present the application of the high vertical resolution azimuthal resistivity imaging, to identify productive zones within highly shale laminated sand intervals of the upper C reservoir in Area 2 of Ceuta field in Lake Maracaibo.

The deposition of the upper C Eocene Misoa Formation in this area, took place in a complex set of environments including valley fill and tidal-dominated, lower delta plain settings. It exhibits a sequence of oil-saturated shaly sands and shale bodies. The sands bodies are characterized by a series of thin sedimentary facies of very fine to medium sand grains, and they are vertically separated by small shale laminates. These complex characteristics of the sand intervals make very difficult the selection of pay zones through the application of conventional resistivity tools, which are adversely affected by their limited vertical resolution. These tools fail in the detection of thin sand and consequently they register a low average resistivity for a vertically stacked interval of thin sa ds and shales, which indicates high water saturation when standard saturation models are applied.

The characterization and selection of pay intervals in the new wells have been accomplished by the acquisition and interpretation of high vertical resolution azimuthal resistivity images, which provide a significant definition of the true resistivities of thin sands and proved to be a tool to enhance the results of the petrophysical evaluation of this type of reservoir.

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