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The AAPG/Datapages Combined Publications Database

Journal of Petroleum Geology


Journal of Petroleum Geology, vol.27 (4), October 2004, pp 335-355
Copyright copyrght.jpg (4253 bytes) 2004 by Scientific Press Ltd. All rights reserved.


G. H. Lee*#, M. A. Eissa**, C. L. Decker**1, J. P. Castagna**, D. J. O’Meara** and H. D. Mar?n***

*Dept of Environmental Exploration Engineering, Pukyong National University, Busan 608-737, Korea.

** Institute for Exploration and Development Geosciences, University of Oklahoma, Norman, Oklahoma 73019, USA.

1Current address: Gas Technology Institute, Houston, Texas 77090, USA.

*** Tecpetrol, Buenos Aires, Argentina.

# Corresponding Author, email: [email protected]

The principal reservoirs in the Bermejo oilfield in the NW Oriente Basin of Ecuador are the Cretaceous Holl�n Formation and the basal sandstone in the Tena Formation (“basal Tena sand”). Analysis of 3D seismic and wireline log data suggests that much of the Holl�n Formation consists of stacked fluvial channel deposits. In the overlying Napo Formation, the excellent correlation of log signatures, continuous seismic reflections, and the absence of thick sandstone layers (except for the coarsening-upward Napo “T” sand), suggest deposition from uniform processes, possibly in a shelf environment. The upper Napo and lower Tena Formations are interpreted as a series of transgressive deposits, punctuated by the basal Tena sand. Truncation in the Holl�n Formation is better observed on east-west seismic lines than on north-south seismic lines, suggesting a north-south trending fluvial system. This, together with the northward thinning of the top Holl�n shale suggesting an east-west trending palaeo-shorezone, further predicts north-south oriented reservoir distribution. The palaeogeography of the Oriente Basin was probably more complex than that portrayed in previous depositional models which depict a north-south oriented palaeo-shorezone and sediment supply from the east. Detailed depth structure maps reveal structural closures that have not been tested.

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