Controls on Oligocene-Miocene carbonate shelf evolution, offshore East Java, Indonesia : insights from architecture, facies, and seismic geomorphology

Carbonates were extensively deposited in the Oligocene–Miocene and are now prolific hydrocarbon reservoirs in the Southeast Asia region. Hydrocarbon exploration and production activities have resulted in extensive availability of subsurface data from this stratigraphic interval. During the Oligocene–Miocene, carbonate shelves in this region have evolved and show spatial-temporal variations in term of architecture and facies. Despite the economic importance, data availability, and complexity of the region, little effort has been made to decipher the dominant controls on carbonate shelves evolution. This research utilized 24 wells and 1,300 km² of 3D seismic data from offshore East Java, Indonesia to study the Oligocene–Early Miocene Kujung Formation and the Late Miocene Wonocolo Formation. Depositional settings of the Kujung Formation have evolved from mixed-siliciclastic-carbonate shelf in the Rupelian–Chattian to carbonate-buildups shelf in the Aquitanian. The change happened at around the Oligocene-Miocene boundary at 23 Ma. Three-dimensional seismic geomorphology techniques were utilized to further characterize the Kujung and Wonocolo Formations. Carbonate shelves in the study area have evolved from having west-southwest – east-northeast elongated, circular-ovoid, to polygonal carbonate buildups in the Early Miocene to being dominated by north-south elongated flat-topped carbonate platforms in the Late Miocene. Hydrocarbons have been produced mainly from the Kujung Formation buildup-core. On the basis of well data, off-buildup carbonate-dominated strata are considered as an upside potential with indications of gas accumulation. Volumetric calculations demonstrated encouraging results for this interval, which could be developed as part of an integrated field development strategy. Tectonically inherited antecedent topography, siliciclastic sediment routing, and localized differential tectonic subsidence are the dominant controls on platform-, basin-, to regional-scale spatial variation in distribution of siliciclastic and carbonate sediments, and the resulting architecture and facies on carbonate shelves during the Oligocene–Early Miocene. Change in the global sea-level fluctuation patterns seems to have caused the temporal variation represented in extensive carbonate buildups development starting in the Early Miocene. These controls could even override the influence of regional climatic change around the Oligocene-Miocene boundary. In the Late Miocene, intensifying compressional tectonic events have resulted in decreased accommodation on the carbonate shelves. Development of Indonesian through-flow during this period have strongly influenced the oceanic circulation resulted in extensive development of north-south elongated flat-topped carbonate platforms. Ultimately, this research aims to provide valuable insights to better explain controls on Oligocene-Miocene carbonate shelf evolution and to better predict architecture, facies, geometry, and distribution of carbonate reservoirs situated in a tectonically active region. This research utilized 24 wells and 1,300 km2 of 3D seismic data from offshore East Java, Indonesia to study the Oligocene–Early Miocene Kujung Formation and the Late Miocene Wonocolo Formation. Depositional settings of the Kujung Formation have evolved from mixed-siliciclastic-carbonate shelf in the Rupelian–Chattian to carbonate-buildups shelf in the Aquitanian. The change happened at around the Oligocene-Miocene boundary at 23 Ma. Three-dimensional seismic geomorphology techniques were utilized to further characterize the Kujung and Wonocolo Formations. Carbonate shelves in the study area have evolved from having west-southwest – east-northeast elongated, circular-ovoid, to polygonal carbonate buildups in the Early Miocene to being dominated by north-south elongated flat-topped carbonate platforms in the Late Miocene. Hydrocarbons have been produced mainly from the Kujung Formation buildup-core. On the basis of well data, off-buildup carbonate-dominated strata are considered as an upside potential with indications of gas accumulation. Volumetric calculations demonstrated encouraging results for this interval, which could be developed as part of an integrated field development strategy. Tectonically inherited antecedent topography, siliciclastic sediment routing, and localized differential tectonic subsidence are the dominant controls on platform-, basin-, to regional-scale spatial variation in distribution of siliciclastic and carbonate sediments, and the resulting architecture and facies on carbonate shelves during the Oligocene–Early Miocene. Change in the global sea-level fluctuation patterns seems to have caused the temporal variation represented in extensive carbonate buildups development starting in the Early Miocene. These controls could even override the influence of regional climatic change around the Oligocene-Miocene boundary. In the Late Miocene, intensifying compressional tectonic events have resulted in decreased accommodation on the carbonate shelves. Development of Indonesian through-flow during this period have strongly influenced the oceanic circulation resulted in extensive development of north-south elongated flat-topped carbonate platforms. Ultimately, this research aims to provide valuable insights to better explain controls on Oligocene-Miocene carbonate shelf evolution and to better predict architecture, facies, geometry, and distribution of carbonate reservoirs situated in a tectonically active region.