CASAS, JOHNNY E., and FERNANDO CHACARTEGUI, Maraven S.A., Caracas, Venezuela

ABSTRACT: Sedimentological and Diagenetic Study of Lower Misoa (C6i and C7 Members) in Lama Field, Maracaibo Lake, Venezuela

This sedimentological study describes the Lower Misoa Formation in the Lama Field and is a part of a project to simulate the reservoirs for E.O.R. purposes. The reservoirs were cored in four wells for a total of 1500 feet. The Lower Misoa (C6i to C7) is divided into six sedimentary units, four corresponding to C7 and the other two within C6i. Using integrated sedimentological and petrophysical data, four flow units are defined, two within C7 and two within C6i. Sporomorphus species observed at the top of C7, identify this unit as the palynological zone M corresponding to Lower Eocene. By defining sedimentary units using log character, it is possible to construct trend surface and isopach maps that show the geometry of the reservoir as an elongated body with a northeast-southwest orien ation. Petrophysical and petrographical characterization of facies suggest that sedimentary facies, control the variations observed in permeability, porosity and oil accumulation in the reservoir. The most important diagenetic alterations are carbonate cementation, silica overgrowths and kaolinite precipitation. For the reservoir C6i the flow unit with the best performance is the number III characterized by f = 23 % and K = 300 md. For C7 which is the best Lower Misoa reservoir in the field, the flow unit II has the best performance with f = 25 % and K = 600 md. Characteristics such as primary sedimentary structures, lithofacies analysis and the floral-faunal analysis of samples, suggest that this sequences were deposited as a large barrier island complex with extensive coastal lagoons.< P>

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