Sedimentary and Tectonic Controls on Oil Occurrences in the Traditional Producing Area, Barinas Subbasin, Western Venezuela: ABSTRACT

Abstract

A Stratigraphic and Tectonic model explains the oil-field locations in the Traditional Producing Area of the Barinas Subbasin, Western Venezuela. The database for the model includes a 585-km[sup 2] 3-D seismic survey, as well as petrophysical, lithologic and biostratigraphic data from Cretaceous and Tertiary sediments. A long-term relative sea level rise from Albian through Campanian (Cretaceous) time, coincident with passive-margin basin subsidence, resulted in onlap of marginal marine sands and marine-shelf limestones and shales over crystalline metamorphic rocks of the Guayana Shield Basement. Facies changes in the Cretaceous Aguardiente, Escandalosa, and Navay Formations are related mainly to eustatic sea level changes. A tectonic pulse deformed these sediments in Late Maastrichtian to Paleocene time. An erosional unconformity that developed atop this deformed Cretaceous section relates to tectonic uplift and not to sea-level change. Onlap of Middle Eocene marine transgressive Gobernador Fm. sands and Masparrito Fm. limestones over this unconformity was driven by increased tectonic subsidence. Accelerated tectonic subsidence drowned the Masparrito carbonate platform and led to deposition of a condensed section within the lower Paguey Formation; this condensed section marks a tectonic Maximum Flooding Surface not related to eustatic sea level change. After deposition of the Eocene Paguey, and just priormore » to deposition of the Oligo-Miocene Parangula Formation, a second tectonic event reactivated older faults and led to growth of structural traps for Cretaceous and Eocene reservoirs. Both tectonic and eustatic events have combined to control oil occurrence in the Barinas Subbasin.« less