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Delgado, Manuel1
(1) PDVSA E y P, Puerto La Cruz, Venezuela

ABSTRACT: Stratigraphic and Sedimentologic Model of the Lower to Middle Miocene, U3 Sandstone (Merecure Formation) to M3-M4 Sandstones (Oficina Formation), Chimire-Boca Field, Anzoátegui State, Eastern Venezuela

The stratigraphic and sedimentologic model presented in this study was based on the interpretation of 767 feet of cores and well log characteristics of well A1 (Chimire-Boca Field, Anzoátegui State). Stratigraphically, the interval comprises the Lower to Middle Miocene: Merecure Formation (U3 sandstone) to the M3/M4 sandstones of the Oficina Formation. The objective is to stablish the geometry, orientation and phisycal quality of the sedimentary deposits to contribute to the selection of an appropiate exploitation plan. The stratigraphic section was divided in two sequences separated by a Maximun Flooding Surface: a lower sandy sequence (Merecure Formation); and an upper shaly and heterolithic sequence (Oficina Formation). A total of nine regressive/transgressive parasequence "sets" were recognized: two in the lower interval and seven in the upper one, of a transgressive character. Macroscopic core description allows identification of fifteen sedimentary lithofacies: 1.-Six sandy lithofacies (S/S3/S11/S2/S21/S22; and their bioturbated counterparts SB/S3B/S2B); 2.- Two heterolithic lithofacies (H/HB); 3.-Two shaly lithofacies (L/L1); 4.-One coal to coaly shale lithofacies (C) and 5.-One Paleosoil facies (P). This sedimentary facies can be grouped in five distinctive sedimentary facies associations: fluvial channels, crevasse splay, mouth bars/delta front and bay/shallow marine. Permeability and shale volume allow definition of three quality rock types: Type A/excelent quality rock (S/S3), Type B/moderate quality rock (S11) and Type C/ moderate to poor quality rock (S2/S21/S22 and bioturbated sandstones). Based on lithofacies analysis, ichnofacies, fossil content and sedimentological parameters, the Merecure and Oficina Formations sandstones are interpreted as deposited in a fluvial environment and in a fluvial dominated deltaic environment, respectively.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.