Abstract: Structural Framework Evolution and Timing of Oil Accumulations, Traditional Areas, Barinas Subbasin, Western Venezuela

Julieta Daal, J. Salas, M. Lopez, G. Martinez, A. Marquez, J. B. Dunham

A 3D seismic survey is used in the definition of the tectonic and stratigraphic evolution, and timing of oil generation and migration in the traditional producing areas of the Barinas Subbasin of western Venezuela. The database consisted of an 885-km² seismic survey, calibrated with core, sidewall and ditch sample analyses from Cretaceous and Tertiary sequences.

Seismic to well data calibration was achieved through time-depth conversions, based on synthetic seismograms. Two approaches were followed in the construction of the synthetic seismograms. For wells with available sonic and density curves, synthetic seismograms were constructed directly through a commercial software. For wells with no sonic or density curves available, the Barinas-adapted versions of Faust's and Gardner's equations were used to construct synthetic seismograms from the deep resistivity curves. In both cases, excellent seismic-well log correlations were achieved, even in the more complex structures.

Flattenings at different seismic reflectors were used to determine the evolution of stratigraphic and tectonic features. Onlaps, downlaps and toplaps are described in the seismic, and their relations with the tectonic and stratigraphic evolution were interpreted. Two major tectonic regimes were identified. The first regime is that of a Cretaceous marine shelf passive margin. The second one corresponds to the formation and filling of two Tertiary foreland basins. Present structures were already formed when the main episodes of oil generation and migration occurred.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela