Abstract

Previous well correlation and detailed reservoir characterization of Baong Sands of North Sumatra Basin were difficult owing to rapid facies changes. A different approach was tried by using 2D - 3D seismic and well log data in a fully integrated interpretation of sequence stratigraphy, facies distribution and reservoir characterization.

The Baong Sand, whose ages are variable in different parts of the basin, have been divided into lower and middle sand members of Middle Miocene age. The lower Baong Sandstone was sourced from the Malacca Platform. This unit was interpreted as highstand to shelf margin-system tract, prograding southward from the platform. A shift in the direction of sediment supply from a northern source (Malacca) to a southern one (Barisan) and the drop of sea level resulted in the deposition of lowstand system tract unit of Middle Baong Sand in the southern area. The differences of these two sand members are clearly defined from seismic model, sand provenance and well correlation.

The distribution of potential reservoirs could be mapped in detail by 2D seismic facies analysis and well log data interpretation which were guided by lowstand-shelf margin/highstand reservoir development model. Analyses from 2D seismic inversion and 3D seismic time-horizon slices produced detailed maps of individual reservoir units.

Results of the study suggested that the prograding shelf margin, the highstand system tract, is a less attractive exploration target due to thinner sand thickness developed in poor quality reservoirs. The lowstand, which produced medium thickness, good quality sand reservoirs, is obviously the target for exploration and development.