Abstract:
North Papua Basin is a forearc basin located in the North Papua, Indonesia. The basin has been categorized as frontier basin due to limited exploration activities. There have been 10 wells drilled since 1950, 5 wells of which are dry, 1 well with oil and gas show, and 4 wells were plugged and abandoned due to overpressure. Nevertheless, hydrocarbons have occurred within the basin as indicated by one well with hydrocarbon shows and the presence of famous oil seep of the Teer River. This study will show new results of geochemical analyses of the oil seep and petroleum system evaluation, improving the basin’s prospectivity. The oil seep has been sampled and analysed for their biomarkers using gas chromatography (GC) and gas chromatography/ mass spectrometry (GC/ MS) of saturate triterpanes m/z 191, steranes m/z 217, and aromatic methyl phenanthrene (m/z 178 and m/z 192). The oil seep is minor biodegraded based on the distribution of n-alkanes. The isoprenoid pristane/ phytane ratio indicates that the oil was generated from shaly to coally source rocks deposited in low reduction environment. High peak of Oleanane from triterpanes and the appearance of Bicadinanes from steranes conclude that the source rocks are Miocene in age at the oldest, from kerogen type III. Based on methyl phenanthrene distribution, the oil was generated from a maturity equivalent with Ro of 0.9 (optimum maturity). Based on geochemical analyses and geologic setting of the North Papua Basin, the strongest candidates for the active source rocks are those within the Middle- Late Miocene Makats and/or Early Pliocene Memberamo “B” Formations. The sediments of both formations were deposited in terestrial to transition/estuarine environments which fit with the oil characteristics. Based on thermal maturity profiles of existing wells, the depth of around 4,000 m is the top of oil window in the area. The presence of source rocks generating oils as shown by the oil seep of the Teer River is the most important element and process of the petroleum system of this area. Other elements and processes of petroleum systems including reservoirs, seal rocks and trap formation exist in the basin based on the geologic setting but need further data and studies to resolve. These provide opportunities for petroleum exploration in North Papua Basin which so far has been under-explored. Keywords: North Papua Basin, Makats and Memberamo “B” Formations, Teer River oil seep, geochemistry, petroleum system evaluation.
