Depositional environments and source rock investigations of the Oligocene to Middle Miocene deposits in the Ardjuna Basin, offshore Northwest Java, Indonesia

Investigations of depositional environments, paleogeographic evolution, source rock potential/maturity, and petroleum generation, expulsion, migration and accumulation were performed on the Oligocene to Middle Miocene deposits in the Ardjuna Basin, offshore Northwest Java, using integrated geologic, seismic and geochemical approaches.;The Oligocene to Middle Miocene sediments were deposited in a generally transgressive sequence. It is the most prospective stratigraphic unit for petroleum exploration in the Ardjuna Basin. The rocks comprise three Formations: Talang Akar, Baturaja and Cibulakan. Talang Akar sediments were deposited in a deltaic to shore environment, Baturaja carbonates were formed on a warm and flat shelf, and Cibulakan sediments were deposited mostly in the inner to outer shelf environment. Paleogeography of six stages within the study interval, showing the degree of marine transgression were mapped based on integrated biostratigraphic, paleoenvironmental, and seismic-stratigraphic data.;The coals and carbonaceous shales deposited in the deltaic and nearshore environment of the Talang Akar Formation are petroleum source rocks for the waxy oils produced in the Ardjuna Basin. The organic matter contains predominantly vitrinite maceral and up to 30% exinite maceral.;Source rock temperature, after calibration with vitrinite reflectance, provides an accurate quantitative measurement for predicting the level of thermal maturation. This compensates for the ambiguity of using depth as maturation indicator, particularly in areas with a wide range of geothermal gradients (2;Two geochemical approaches were used and compared in petroleum resource assessment: petroleum yield (S1) method and genetic potential (S2) method. The oil generative kitchen, the Ardjuna depocenter, has the best opportunity for new oil discovery. This model has since been proved by subsequent drilling leading to several oil discoveries in last two years.