Abstract: Diachroneity of Early Cretaceous (Aptian-Albian) Reservoir Rocks in the Oriente Basin, Ecuador: Implications for Oil Exploration

VILLAGOMEZ, ROMMEL A., Saint Louis University, Dept. of Earth and Atmospheric Sciences, St. Louis, MO

Cretaceous formations in the Oriente Basin in Ecuador have produced more than 3 billion bbl of oil in the last 20 years. These formations have been divided into different informal stratigraphic units that are easily recognized on well logs throughout the Oriente Basin. Recent biostratigraphic data show, however, that the Hollin Formation (Early Cretaceous) is diachronous, resulting in inaccurate correlations.

This study has found that the Hollin Formation can be divided biostratigraphically into two different reservoirs of distinct ages. The Early Aptian is restricted to the central-eastern part of the Oriente Basin and is characteristically a saltwater bearing sandstone. Late Aptian-Early Albian fluvio-deltaic and Middle Albian shallow marine deposits, in contrast, are located in the central-western part of the basin and contain fresh water. These two different reservoirs are separated by a "Mid"-Aptian marine shale unit.

The Early Aptian has remain unrecognized previously because of the few wells that penetrate the entire Cretaceous sequence, the lack of precise biostratigraphic data, and the partial erosion of the "Mid"-Aptian shale unit which makes the Early Aptian indistinguishable from the Late Aptian strata. Reconnaissance and exploration of the Early Aptian reservoir can open new possibilities for the discovery of oil in the Oriente Basin.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid