Aracas Field - reservoir heterogeneities and secondary recovery performance

In the Aracas Field (Reconcavo Basin, Brazil), the Sergi Formation held ca. 30% of the 60 x 106 cu m of the field's original oil in place. However, its contribution for the field (Upper Jurassic) is a braided-stream sequence of conglomeratic and coarse to very fine-grained sandstones and minor siltstone and shale layers with an average thickness of 215 m. Primary recovery started in 1967. The water injection was initiated in 1973 and neither improved the production nor repressured the reservoir to the expected levels. To date, only 8% of the estimated original oil in place has been recovered from this pool. The Sergi Formation was cored in 2 new wells. Pressure data from new wells and geological analysis derived from log and core interpretation strongly suggest that the present peripheral injection-well pattern is insufficient and that an infill drilling program could contribute to a more effective pressure maintenance.