Geology of the Jurassic gas discoveries in Bintuni Bay, Western Irian Jaya

Abstract

Abstract The Roabiba-1 well, drilled by Occidental, Nippon Oil Exploration, and Sun in Bintuni Bay in 1990, tested 23.6 MMSCFGPD from a Middle Jurassic sandstone and was the first significant Mesozoic hydrocarbon discovery in Indonesia. Two additional Jurassic gas discoveries were made in 1992. The results of the exploration drilling and acquisition of over 14,000 km. of marine seismic by the Occidental Group have been interpreted with the following conclusions: 1. The gas is trapped in northwesterly trending anticlines formed by Late Miocene and younger compression and associated left-lateral wrench faulting. 2. The main gas reservoirs consist of massive, post-rift, Jurassic fluvio-deltaic sandstones which were deposited in an east-west trending belt extending through Bintuni Bay. The gas reservoirs contain low porosity due to extensive quartz overgrowth cementation, which is believed to be caused by a high degree of compaction. 3. Source rocks have been identified in the Permian, Jurassic, and Tertiary sections. The Permian and Jurassic source rocks are dominated by nonmarine kerogens which are gas prone with some oil potential. The gas and condensate in the Jurassic reservoirs are most likely derived from these source rocks. The Tertiary source rocks are dominated by marine algal sapropel and are oil prone. The oils tested in the New Guinea Limestone, with the possible exception of Wiriagar, appear to be derived from Tertiary source rocks. 4. The gas in the Bintuni Bay discovery wells is very lean and is derived from highly mature source rocks. An unusually heavy condensate recovered from Roabiba-1 is derived from a middle mature source rock and is interpreted to be an oil which was fractionated by gas. 5. The present day kitchen areas for pre-Tertiary source rocks are located in the Bintuni and Berau Basins. The gas appears to have migrated northwesterly along regional anticlines from the deepest, southeastern part of the Bintuni Basin within the last five million years.