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GRUBER, IRAIMA, MOISES UZCATEGUI, MARITZA JIMENEZ, ROBERTO ARSTEIN, and FRANKLIN RUIZ, Corpoven, S.A., Puerto La Cruz, Venezuela

ABSTRACT: Verification of the Sedimentological Model of the Lower and Middle Miocene in Southwest Oficina, Venezuela, Using Seismic Inversion Methods

The study area is located on the southern flank of the eastern Venezuelan basin, southwest of the traditional Oficina fields and covers an area of 160 sq km. The sedimentary section is comprised of cretaceous, oligocene and miocene age deposits.

Based on lithological, electrofacies and core studies, a sedimentological model has been developed for the lower to middle miocene oficina formation which comprises the essential oil-producing horizon in this area. The oficina formation forms a sedimentary unit 1340 m thick, developed on a gently subsiding ramp-type shelf which forms the passive margin of a large foreland basin.

The general depositional setting varied form shelf to coastal-deltaic, and the section exhibits a number of parasequence-like small scale regressive-transgressive deltaic cycles. The major reservoir sandstones comprise several types of deltaic depositional facies: distributary channels, channel-mouth bars, and crevasse splays. In addition, a number of regionally widespread incised valley deposits have been identified, these represent fluvial and deltaic channel fills the major shale deposits correspond to interdistributary bay and prodelta/shelf environments.

This sedimentological model was verified by using seismic inversion methods on selected seismic lines which showed the spatial relationships of these stratigraphic-sedimentological units, including sand body continuity. The model has enabled the location of sands to be predicted in areas which are in the early stages of development, to optimize the recovery in mature fields, and has been used to select a further 60 drilling locations of which have been completed successfully.

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