Publications

Oligocene carbonate plays in the Upper Kutai Basin are under-explored, with exploration historically focusing on the Miocene deltaic and turbidite plays. These carbonates mainly consist of the Berai Formation which outcrops along the southern basin margin, and is seismically imaged in the subsurface, forming on isolated basement highs and large platform areas. The Kerendan Field in the Bangkanai PSC is the only Oligocene carbonate hydrocarbon accumulation in the basin, comprising c. 100km2 of structural - stratigraphic highs with two culminations. The western culmination was recently proved to be gas bearing by the West Kerendan-1 exploration well located 11 kms southwest of the Kerendan-1 discovery. Development drilling on the Kerendan Field and the West Kerendan-1 exploration well has provided new information which, together with a re-evaluation of the existing well core data and 2D seismic coverage has led to a reinterpretation of the reservoir depositional model. It was previously characterized as an atoll with outer slope, rim and internal lagoonal facies (Saller and Vijaya, 2002). An alternative interpretation is proposed with a more open platform or bank and a partially developed rim. Platform, reef and carbonate sand facies were deposited in a range of shallow to deeper photic water depths, under mainly low to moderate energy conditions within a semi enclosed marine embayment. Pressure and well test data show reservoir quality rocks across the entire Kerendan structure and a common gas-water contact. Where identified on regional 2D seismic coverage in the area of the Bangkanai and West Bangkanai PSCs, the Oligocene carbonate sequence sit on NNE-SSW trending Paleogene horsts. Bi-directional down-lapping features with parallel, mounded or chaotic internal seismic reflectors are observed in the carbonates suggesting reservoirs similar to the Kerendan area. Several of these highs are undrilled and represent targets for future exploration efforts including additional 2D seismic acquisition.