Paleogeography of the Oligocene in Northeastern Guárico State, Eastern Venezuelan Basin

Delgado, Manuel¹, Jair Carvajal² (1) PDVSA División Oriente, Guanta, Venezuela (2) Universidad de Oriente, Guanta, Venezuela

The paleogeographycal model presented in this study is based on the interpretation of 785’ of cores from six wells and well log data from fifteen wells (Yucal-Placer Oilield, Gu¨¢rico State). Stratigraphically the interval comprises the Oligocene La Pascua and Roblecito formations. The geometry, orientation and phisycal quality of the sedimentary deposits are established in order to contribute with the exploration projects undertaken in this area.

Macroscopic core description allows identification of the following sedimentary lithofa­cies: 1.- Seven sandy lithofacies (CG/S/S3/S3M/S11/S2/S21; and their bioturbated counter­parts S11B/S2B); 2.- One heterolithic lithofacies (H); 3.- Two shaly lithofacies (L/ST; and their bioturbated counterparts STB) and 4.- One Paleosoil (P) facies.

This sedimentary facies are grouped in five sedimentary facies associations: fluvial dis­tributary channel, crevasse splay, mouth bar/delta front, medium to upper shoreface and bay/offshore.

Permeability and porosity values (K<2.5 mD and º < 16 %) are very low for all the litho­facies. However, the S3/S3M/S11/S2/S1 lithofacies have the higher permeability and poros­ity values (2.5 mD>K>1 mD and º > 8%) and the lower shale volume values (< 40 %).

On the basis of lithofacies analysis, ichnofacies, fossil content and sedimentological parameters, the studied interval of the La Pascua and Roblecito formations are interpreted as deposited in a fluvial dominated deltaic environment, with an important influence of wave energy. Paleogeographycal maps show that the main sediment input is from the north­northwest to the south-southeast direction, and their variations are controlled by the east­ward movement of the Caribbean tectonic plate.