Publications

The Makassar Strait - South Makassar Basin area has several hydrocarbon-bearing wells, including gas and condensate from the Ruby Field, oil from Pangkat-1, and gas from Sultan-1. These confirm the presence of a working petroleum system in the area. TOC and Rock Eval pyrolysis data from Kelara-1, Makassar Straits-1, Martaban-1 and Pangkat-1 were used in this study to examine source rock facies within the Eocene. The dominant organofacies are Type D/E fluvio-deltaic coals and minor Type C lacustrine shales within the Middle Eocene. In contrast, the Late Eocene section has little or no source potential. Net source from logs and seismic mapping was used to interpret Middle Eocene source rock distribution and thickness. Temperatures were derived from bottom hole log temperatures taken during wireline logging operations and corrected using Horner plots. Corrected temperatures were modeled using transient, fixed temperature at base lithosphere. Optimized model temperatures vs. depth solutions for a consistent set of input criteria (variable crustal thickness) closely match calibrated data and reflect a fairly broad range of subsurface thermal gradients in the area. The commencement of hydrocarbon generation and expulsion is approximately 20 Ma within the South Makassar Basin and 12 Ma in the Pangkat Graben. Based on seismic mapping and calibration with biostratigraphy and sedimentology, the regional seal facies are Middle Miocene pro-delta shales that * Mubadala Petroleum, Jakarta, Indonesia prograded from west to east across the Paternoster Platform and into the basin. These shales began deposition over the Ruby Field at approximately 12 Ma and are progressively younger in the basin. Therefore, it is postulated that timing of hydrocarbon generation relative to seal emplacement may have been a critical risk factor for Sultan-1 located in a deeper part of the basin. This is consistent with published ages of reservoir and seal and may be consistent with an underfilled trap. The phase of the hydrocarbon in Ruby Field is predominantly gas with minor condensate. Based on isotopic analysis of Makassar Straits-3 gas, it is concluded that the gas is a mixture of biogenic and thermogenic components. Keywords: Source rock and thermal calibration, South Makassar Basin, Timing of generation and expulsion