Coal as a Petroleum Source Rock Brown Shale Coal Zone Based on Macerals and Geochemistry Analysis, Kiliranjau, Sijunjung Regency, West Sumatera, Indonesia

The study area encompasses the Kiliranjao Sub Basin, situated within the broader context of the Central Sumatra Basin in the West-Northwest region. This study focuses on analyzing the Coal Seam within the Brown Shale Formation of the Eocene-Oligocene Pematang Group. In the Central Sumatra Basin, the majority of the Brown Shale oil source rock is derived from the Paleogene lacustrine shale rock of the Brown Shale Formation. Notably, this research unveils the presence of exsudatinite maceral within a coal seam, suggesting that coal derived from the Brown Shale serves as an oil source rock, characterized by random vitrinite reflectance values ranging between 0.36 and 0.51 (immature stage). The findings from rock eval pyrolysis of the coal yield significant insights. The correlation between the Hydrogen Index and Total Organic Carbon values indicates a very good to excellent quality of source rock. Additionally, the correlation between S2 and Total Organic Carbon values suggests a high richness and quantity of the source material, also rated as very good to excellent. The correlation of the Hydrogen Index with Temperature Maximum indicates an immature state of the coal unit classified as C immature. Furthermore, the correlation between the Hydrogen Index and Oxygen Index signifies the coal's propensity for oil generation (kerogen type II) and gas generation (kerogen type III). Hence, the presence of exudatinite maceral alongside the results from the pyrolysis rock eval analysis conclusively affirms the coal seam's status as an oil source rock, having undergone bituminization in the process of oil formation.