Reef exploration in the East Seng-kang basin Sulawesi.

Abstract

Abstract Reconnaissance seismic shot in 1971/72 showed a number of well defined seismic anomalies within the East Sengkang Basin which were interpreted as buried reefs. Subsequent fieldwork revealed that Late Miocene reefs outcropped along the southern margin of the basin. A drilling programme in 1975 and 1976 proved the presence of three, shallow, gas-bearing, Late Miocene reefs in the northern part of the basin. Seismic acquisition and drilling have proved the economic significance of these discoveries, with four separate accumulations containing about 0.75 TCF of dry gas in place at an average depth of 700 m. Kampung Baru is the largest field and contains over half the total. Reservoir quality and gas deliverability are excellent. The gas was probably generated in the West Sengkang Basin and sub-sequently migrated into the East Sengkang Basin. Deposition in the East Sengkang Basin probably started during the Early Miocene. A sequence of Lower Miocene mudstones and limestones unconformably overlies acoustic basement consisting of Eocene volcanics. During the tectonically active Middle Miocene, deposition was interrupted by two periods of deformation and erosion. Carbonate deposition became established in the Late Miocene and platform limestones were widespread throughout the East Sengkang Basin. Thick pinnacle reef complexes developed above the platform in areas where reef growth could keep pace with the relative rise in sea level. Reef growth ceased at the end of the Miocene. Subsequent renewed clastic sedimentation covered the irregular limestone surface. Late Pliocene regression culminated in the Holocene with erosion.