Publications

The Offshore Berau area is located about 100 km west of the Tangguh area in Bird's Head, Papua. Exploration activities in the area have been dormant, even though a multi-tcf gas has been discovered in the nearby Tangguh fields. Several exploration wells targeted the Pre-Tertiary reservoir, which has revealed hydrocarbon, but no commercial accumulation has thus far been discovered. This paper offers a comprehensive evaluation of the petroleum systems in the Pre-Tertiary interval of the offshore Berau area, in order to understand the potential. This study suggests that all petroleum system elements are working in the Berau basin. The biggest risk is the maturity level of the source rock in the Berau basin. However, the presence of any older source rock in the basin, and another, possibly deeper kitchen to the south, could make the area more attractive. Stratigraphically, three mega sequences can be defined: (1) Pre-rift sequence, which consists of Pre-Permian age sediment and meta-sediment, (2) Permian to Triassic syn-rift sequence, composed of fluvio-deltaic sediments, and (3) Post-rift sequence of Jurassic to Tertiary passive margin deposits. The primary reservoir target is the Jurassic transgressive sandstones, equivalent to the main reservoir in the Tangguh fields (although thinner and more distal marine sands have been penetrated in wells in the Offshore Berau area). Multiple source rocks are present, and can potentially generate multi-tcf gas. The Jurassic shale potentially generates a significant amount of gas, and a small amount of oil as well. Additionally, Jurassic coals and Permian coals could potentially generate a significant amount of gas. Our study suggests that the Jurassic and Permian source rock interval in the Berau basin is in fact already in the oil window, and that the source is typed as 'gasprone'. This combination explains the lack of hydrocarbons yet discovered in the region. Four main focuses of migration from the Berau basin were identified, based on lateral migration models, on top of the Jurassic interval. Three of these migration focuses have not yet been tested.