ASPECTS OF THE PETROLEUM GEOLOGY OF THE BERMEJO FIELD, NORTHWESTERN ORIENTE BASIN, ECUADOR

The principal reservoirs in the Bermejo oilfield in the NW Oriente Basin of Ecuador are the Cretaceous Hollin 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 Hollin 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 Hollín 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 Hollín 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.