Publications

The Belumai Formation, North Sumatera Basin, is Lower Miocene sandstones with shallow to open marine environment (inner to outer neritic). The type section of the Belumai Sandstone was found in the Belumai area, 60 km South of Medan city. It was described as a glauconitic sandstone, fine to medium grained, occasionally intercalated with stony marl and argillaceous sandstone. This formation is a proven hydrocarbon reservoir with its sandstone packages of at least 100 meters thick. Previous regional studies of the formation have been based primarily on field work and well data, resulted in varying paleomorphological interpretations. A Study area was restricted to the North and East offshore region of the basin. The paleomorphic features of Belumai depositional systems can be distinguished from 3D seismic data and stratigraphic correlations from well data. Nearly 450 km2 of 3D seismic survey, along with data from 5 wells and a core were reviewed and key outcrop sections analyzed in detail. Depositional features were analyzed from both horizon slices and windowed attribute extractions in a flattened volume within a stratigraphic sequence. Facies can be inferred from the resulting interpreted maps, which basically confine the variation in seismic reflections caused by geology change. The interpretation shows during Belumai deposition, sandstones were localized as lower-upper shore face to foreshore sandbars at well Y-3. Seismic images of reservoir from Y gas field show strong amplitude features and were related to coarsening upward type log pattern. Interesting barrier sand and also nearshore system depositional features were observed at northern part of the study area. This study demonstrates how to deploy seismic paleomorphology and seismic attributes extraction to build a model of the Belumai formation facies. The results of these methods are used to recognize geologically significant stratigraphic and paleomorphologic patterns and predict lithological distribution based on seismic patterns.