Publications

Letang, Rawa and Tengah are gas fields discovered in the early 90s with carbonate reservoir type of play and they are located within the Corridor Block South Sumatra, trending from SW to the NE, respectively. Tectonic quiescence in the Early Miocene was followed by the development of Batu Raja Formation (BRF) carbonate platform/build-up predominantly above several paleo-high structures as a product of early Tertiary rifting in South Sumatra back-arc basin setting. Observation based on 2D time migrated seismic data sets and ~50 well data as well as full core and side-wall core data from those three fields have led to a significant reservoir characterization which may have far-reaching consequences for presently accepted models.Two main carbonate facies have been recognized across the area, which are the muddy platform facies and the coral-algal reefal buildup facies. The platform facies is predominantly consists of muddy wackestone/packstone facies with less significant porosity contribution to the fluid flow. The reefal build-up facies consists of boundstone to floatstone facies with more typical of reefal organism such as coraline algae. This facies commonly developed above paleo-high structure associated with fault block formation. The deposition of downslope distal facies consists of several brain coral fragment was also developed adjacent to the area where reefal buildup grows. Most of the porosity is within the secondary vuggy and mouldic pore type of leached coral-algal framework. Typical of build-up geometry on Letang, Rawa and Tengah is observed in the seismic section as Late Miocene Telisa shale onlapping onto the BRF. The difference on depositional environment from landward to basinward is shown by the increasing thickness of BRF carbonate from NE to SW. Letang and Tengah have relatively similar isolated platform geometry bounded by faulted margin, where Rawa platform and buildups are coalescences, amalgamated, and expanded through time with isolation of geometry concentrated around the Pre-Tertiary basement high. The carbonate platforms are separated by deep intraplatform channel oriented relatively NW-SE which in some places mimics the basement topography as well.Karstification effect related episodes of subaerial exposure is suggested occurred across the area based on relatively high porosity anomalies that predominantly developed in the upper interval and dies out at some level that mostly within the carbonate platform interior. This interpretation is also supported from several flattened stratigraphic cross section which could also show the possibility of paleogeography of the BRF carbonate during their development. Transgression related with relative sea level rise or probably subsidence related thermal relaxation in the Late Miocene time resulted to shutdown the BRF carbonate factory and subsequently had changed the facies succession into more marine sediments.