Print this pagePotential of Pre-Kais Formation as a Source Rock in the Salawati Basin, Bird Head, West Papua, Indonesia
The Salawati Basin is recognized as the one of big prolific oil basin in Eastern Indonesia with a total cumulative oil production more than 300 million barrel oil. The Klasafet Formation has been assumed as the main hydrocarbon source rock in Salawati Basin deposited in the shallow marine environment during Middle Miocene time.
Several wells that have been drilled in the deepest part of the Salawati Basin show the average of total organic carbon content in Klasafet shales are between 0.4-1%, therefore, it is not match with a total oil produced from the basin. The maturation model from several modeling points in the basin is also indicated that the Klasafet Formation still in the early mature until present day and has not been generated yet hydrocarbon effectively. Therefore, the statement that the Klasafet Formation is the main source rock in the Salawati Basin is still questionable.
The Bagong-1X well drilled in 2007 is the first well has penetrated good oil and gas shows in the pre-Kais sandstones, and also oil has been discovered in the pre-Kais sandstones in SAR-1X exploration well (2008). It indicates that the oil probably has been generated from the pre-Kais shales source rock, it is not from the Mid-Miocene Klasafet shales.
Geochemical analysis of the oil samples from the Bagong-1X and SAR-1X wells indicated that the oil type is waxy (3.57 wt%) with very low sulphur content (0,024-0,028 %), heavy carbon isotope (-22 to -23), pristane/phytane ratio ranges from 1,33-2,61, supported by the occurrences of oleanane as the biomarker of the Tertiary land plants and diahopane/ neohopane as the biomarker of the shallow lacustrine product. Therefore, it is assumed that the oil trapped in the Miocene Intra Kais carbonate reservoir and pre-Kais sandstones was derived from the lacustrine source rock that usually contains very rich of organic carbon content and developed during Early Tertiary time. It will be agreed with a total cumulative oil produced from the Salawati Basin.
The 2D/3D seismic data have identified that the pre-Kais formation deposited in the Early Tertiary half-graben that developed as the tension structure due to the uplifted of Papua area.
However, this assumption is still a hypothesis because up to now there is no well penetrated pre-Kais formation in the deepest part of the graben that expected to be rich of organic carbon.
* Pearl Energy Indonesia
** Institute Technology Bandung
*** Petrochina
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil