COLL, CAROLINA, FERNANDO CHACARTEGUI, OVIDIO SUAREZ, GONZALO ALVAREZ, Maraven, S.A., Caracas, Venezuela, GERARDO MONSEGUI, ROBERTO LAMBERTINI, and PAUL HAINES, Schlumberger, S.A., Caracas, Venezuela

ABSTRACT: High Resolution Evaluation Techniques in Thinly Laminated Shaly Sands

Significant hydrocarbon production may occur from thin layers which were previously considered non- economic. Improved processing methods for detecting and evaluating thin beds have shown these reservoirs to be attractive prospects. Such thinly bedded laminated shale-sand sequences exist within some of the producing formations in Venezuela. These shale sand packages may contain significant bypassed or undeveloped reserves.

A new technique using deconvolution of the deep resistivity through the microresistivity curves (Microlog) identifies potential thinly bedded reservoirs. This methodology appears to be the most reliable permeability indicator of the prospective intervals within the Misoa Formation at Ceuta Field in Maracaibo Lake. The prospective intervals within this field have been calibrated with cores and with sedimentological information.

This calibration shows only two lithofacies contained hydrocarbons previously not evaluated as oil saturated by traditional methods. These facies exhibited low values for deep resistivity curves which indicated high levels of water saturation.

Deep resistivity deconvolution processing has been successfully applied to solve this problem in the Ceuta field. The resulting resistivity curve exhibits a vertical resolution of better than 1 ft, while retaining the essential advantages of deep resistivity curve. Laminated sand analyses were carried out and prove to be very useful in the integration of petrophysical and sedimentological data for detection of prospective intervals.

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