Redefining Horst and Graben Distribution in The Onshore Part of The North East Java Basin and Its New Exploration Opportunity

The onshore part of North East Java Basin (NEJB) is a well-known hydrocarbon producing area in Indonesia, with the largest proven reservoir being the Oligo - Miocene carbonates which accumulated over basement horsts. Currently, the understanding of horst distribution is based on previous publications. However, new integration studies on surface data (e.g. outcrop, satellite image, geological map) and subsurface data (e.g. well data, biostratigraphy, seismic and gravity data) has provided a new perspective of horst and graben distribution, which has led to a new exploration concept in the onshore part of NEJB. The geological character of horst and graben has been carefully described to be used as a predictive tool to redefine where the area should be considered graben or horst. Integrating horst and graben characters with available data has enabled generate of a new horst and graben map. The study outcome suggests there are six horsts and six grabens. Some horsts are known, but many are new. Likewise, some grabens are known, but others are unique. New exploration opportunities have been generated by these horsts and grabens in the context of depositional setting from Middle Eocene to Middle Miocene. In addition, three play concepts have been created. They are Eocene Clastic, Eocene to Early Miocene Carbonates, and Early to Middle Miocene Clastic. The plays differ, since the horst and graben positions are unique compared to traditional knowledge. The message is clear, this study has opened new opportunities, as new horsts mean new opportunities to find new (giant) oil and gas fields.