Stratigraphic and Sedimentological Model of the Mesozoic Section in the El Toco Oilfield, AnzoáTegui State, Eastern Venezuelan Basin

Manuel Delgado, María Espín, and Yasmín Peña
Exploration, PDVSA, Puerto La Cruz, Venezuela

A new oil exploration target has been opened recently in the eastern venezuelan basin by the identification of a possible structural play in the Mesozoic wedge in the El Toco Oilfield (Anzoátegui state). This structure is located within the Espino Graben and is covered by Cretaceous, Oligocene and Miocene strata. This play is probably related to a compressive tectonic event registered after the opening and infilling of the Jurassic rift.

The stratigraphic and sedimentological model presented in this study was based on the interpretation of 767 feet of cores and well log characteristics of well A1. The core intervals are located in the Mesozoic section assigned to the Barranquín Formation. The objective of this study was to establish the stratigraphic and sedimentological framework for this section that have never been drilled before in this area.

Macroscopic core description allows the identification of fourteen sedimentary lithofacies: 1.- Two conglomeratic lithofacies (Cmsa and Cgs), 2.-Eight sandy lithofacies (S4/S/S3/S31/S11/S22/S1 and Sr); 3.- Two limolithic lithofacies (Str and Stl) and 4.-Two shaly lithofacies (L/Lr).

Conventional petrographycal analysis allowed to identify the following sandy microfacies: quartzarenites, quartz wackes, litharenites, sublitharenites lithic wackes, subarkoses and feldespatic wackes. The conglomeratic lithofacies are lithic clast-supported orthoconglomerates and lithic matrix-supported orthoconglomerates.

These sedimentary facies are grouped in four distintive sedimentary facies associations, corresponding to amalgamated braided channels, flood plain, ephemeral lakes and bays.

Based on lithofacies analysis, ichnofacies, fossil content and sedimentological parameters, this section is interpreted as deposited in a proximal to distal prograding braid-delta depositional environment.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas