Generation and Migration of Hydrocarbons from Pre-Tertiary Source Rocks of the Kamundan Area, West Papua, Eastern Indonesia

By

Ory Sadjati¹, N. A. Ascaria¹, A. H. Satyana¹

(1) Pertamina, Jakarta, Indonesia

 The Kamundan area, West Papua, Eastern Indonesia is located to the north of the giant gas field, the Wiriagar Deep, discovered by Arco Indonesia in 1992 within the Jurassic sandstones. This discovery is important for the Kamundan area since showing of how the possible pre-Jurassic source rocks generated and migrated hydrocarbons to the Wiriagar and the Kamundan areas.

To understand generation and migration of hydrocarbons for the Kamundan area, the expected source formation and the Jurassic reservoirs were mapped. The source and gas samples from available wells were geochemically analyzed. Heatflow history reflecting tectonic and source maturation history was generated using BasinMod - 1D and - 2D softwares. The migration routes of the generated hydrocarbons then were modeled.

Thermal modeling carried out for Ayot-2, Tarof-2, and Wiriagar-1 wells show that the sources have been mature since 240-260 Ma (Permo-Triassic). The maturation of the source is considered to relate with rifting subsidence during the Triassic. In 210 Ma (Late Triassic), the hydrocarbons have migrated and charged the whole intervals of the Jurassic reservoirs. Migration kept taking place and charged the Cretaceous reservoir until tectonic activity of the mid-Cretaceous uplifted the area and changed the migration routes. Afterwards, the hydrocarbons re-migrated along the porous beds at the Cretaceous unconformity and charged the Late Cretaceous and the Paleocene reservoirs. This is considered to have caused the significant hydrocarbon accumulation in the Paleocene reservoirs. The study concluded that the petroleum system of the Kamundan area is Permo-Triassic, Jurassic and Paleocene.