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Abstract: Effect of Vertical Heterogeneities in a Petrophysical Evaluation of Low Resistivity Pay Zones, B Sands, Upper Eocene, Block III, Lake Maracaibo

Carolina Coll, Bice Cortiula, Gedi Gonzalez, Elvira Meza, Luis Rondon

Thin-bed reservoirs can exist as intercalations of thin porous beds and shales. For a proper petrophysical evaluation and geological characterization of this type of reservoir it is necessary to implement an integrated analysis, which includes knowledge of the depositional environment to avoid missing oil zones by applying standard petrophysical evaluations. The normal resistivity logs used on this area do not have enough vertical resolution for detecting thin low resistivity pay zones. Consequently, the common water saturation models indicate high water saturation when they are evaluated.

The Middle Eocene Upper B sands are part of the Misoa Formation in Block III of Lake Maracaibo. They have been exploited since 1965 when the first production test was made. The cumulative oil production to date stands at 11.49 MMSTB. In order to supplement the existing geological information in this area, a continuous core was taken which showed the high degree of shales and thin sands intercalations in the pay zone. A careful core-log calibration was made and a new set of petrophysical parameters were established for this reservoir based on the core measurements. This allowed the establishment of a new petrophysical evaluation procedure that helps the calculation of permeability, hydrocarbon volume in place and productivity of this reservoir.

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