View Biostratigraphy as A Useful Tool for Hydrocarbon Exploration – case from the Pre-Tertiary Sediment in the Bird’s Head Region, Papua

Abstrak

Biostratigraphy plays an important role in hydrocarbon exploration as a way to determine sedimentation ages and to give insights into sedimentary environments. However, little is known about the importance of biostratigraphy in hydrocarbon exploration. This paper focuses on the role of biostratigraphy as a useful tool for hydrocarbon exploration to support the search for new hydrocarbon reserves in Indonesia. We presented a case from the Lemigas Stratigraphy Group study on the pre-Tertiary sediment of the Bird’s Head in Papua as an example. This study aims to provide a better understanding of the pre-Tertiary sedimentary stratigraphy by providing a zonal division of age and depositional environment of the sediment of the study area.

The biostratigraphy including foraminiferal, nannoplankton and palynological analyses, was performed on surface samples from the Sungai Ainim traverse, in Ayata Village, Meibrat Region, West Papua and subsurface samples (Wells W-1, S-1, A-2, M-1, O-1, W-4, R-1 and V-1). Overall, this study revealed five chronostratigraphic frameworks, including Permian-Triassic, Middle Jurassic, Late Jurassic, Early Cretaceous, and Late Cretaceous.

The depositional environment initially occurred in a non-marine setting during the Permian-Triassic age. The Early Jurassic age is recorded as a hiatus. Subsequently, the Middle Jurassic is deposited in a nonmarine environment. The environment then shifted to a marine setting during the Late Jurassic age. The sediment succession disappeared during the Early Cretaceous age due to massive erosion. Finally, the Late Cretaceous environment was deposited in a marine setting.

From the biostratigraphic data, we provide an insight into the role of sedimentary age and depositional environment in the framework of petroleum geology. Our findings show that the shale Ainim Formation in the Permian-Triassic age serves as a primary source rock, while the fluvial sandstone of the Tipuma Formation in the Middle Jurassic is considered the main reservoir. The occurrence of deep marine shale formed a caprock during the Late Jurassic age. Finally, the deep marina shale of the Jass Formation in the Late Cretaceous acted as a caprock element in the petroleum system.

The outcome of this research shows that biostratigraphy plays an important role in the construction of geological models for hydrocarbon exploration. It has become a useful tool to support the search for new reserves, especially in the Eastern part of Indonesia.