Jose I. Guzman1
(1) PDVSA-INTEVEP, Los Teques, Venezuela
ABSTRACT: The Lower Lagunillas incised valley network and its control on reservoir heterogeneity in the giant Miocene fields of the Maracaibo Basin, Venezuela
A significant proportion of the known reserves in the Miocene Bolivar Coastal fields of the eastern Maracaibo Basin, is contained in estuarine sediments of a tide-dominated incised valley network which was later prograded by a tide-modified delta system. The incised valleys occur within the basal interval of the Lower Lagunillas member of the Lagunillas Formation.
Incision occurred as a result of tectonic uplift along the northwestern and southwestern margins of the basin during the Early and Middle Miocene. It is best documented in the northeastern sector of the basin, where individual systems are up to 38 meters thick and 2 km wide. The sequence boundary implies a major rearrangement in the nature and orientation of depositional systems, and thus imparts the primary control on the geometry of reservoirs above and below the incision surface. Filling of the valleys occurred primarily during increasing accommodation in the transgressive systems tract, and under the dominant influence of tides that were funneled through a passage connecting the Falcón and Maracaibo basins.
The existence of this incision complex accounts for the stratigraphic boundaries between fields and reservoirs in the area. Mapping of the individual valleys documents the preferential geometry and orientation of reservoir compartments, and may help in planning for horizontal wells and in detecting opportunities for reserve growth in these mature fields.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado