Reef Exploration in Bintuni Basin and Bomberai Trough – Irian Jaya

Abstract The Bintuni Basin is located in western Irian Jaya where exploration has been going on since the early 1930's. However, an active search for Tertiary reefs began recently with the introduction of the Production Sharing Contracts in Indonesia. The Bintuni Basin is a well developed structural – stratigraphic basin having in excess of 22,000' of Tertiary sediments consisting of marine carbonates and shales. In general, the pattern of Tertiary sedimentation in SUN's contract blocks can be envisioned as follows. In early Tertiary times, a broad carbonate platform occupied most of the Bomberai Peninsula. To the east of the platform a basinal area was present in which pelagic limestones were deposited. At the end of Oligocene time, a strong downwarp of the platform margin resulted in the westward migration of the basin and transgression by the Klasafet shales and marls. The westward extension of the basin into the central part of the Bomberai Peninsula has been identified as the Bomberai Trough. Further subsidence took place in Plio-Pleistocene time and this resulted in deposition of a thick sequence of shallow marine clastics. The portion of the platform which subsided and was covered with Klasafet shales and marls is considered to be a likely area for the development of pinnacle reefs. In addition to reefs, the detrital reef carbonates that accumulated along the platform-basin marginal zone, represent excellent hydrocarbon objectives in the area.