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ABSTRACT: Prupuh Oligomiocene carbonate buildup play system in Cepu area, Northeast Java Basin

Koesoemo, Yohannes P. , Oil and Gas Training Center, PPT Migas Cepu, Cepu Central Java, Indonesia

The physiography of Cepu area is included in the Rembang zone of East Java, Indonesia. The tectonic histories of Cepu area can be traced back from late Cretaceous to Resent. The tension of tectonic regime (Paleogen) was continued by compression of tectonic regime (Neogen), and resulted in the main geological structure of the study area. From the seismic section across 20 km south of Kawengan oil field, with north - south direction is showed buildup of Prupuh carbonate is possible over the Cepu high.

Because of the sea level drop 21 m.a., the Prupuh reef exposed and developed secondary porosity in the vadose zone.

As an example of Prupuh carbonate is in Mudi oil field (JOB Pertamina Santa Fe Tuban) located 10 km NE of Bojonegoro. The wells are of natural flow and the types of oil, source oil, heavy oil of high sulphur content. At this time it produces oil of 20.000 BOPD and its cumulative production is 9.4 MM BBLS of oil per July 31 1999. It is approximately 3000 m in depth.

The source of hydrocarbon is possibly from the shale of Ngimbang Formation deposited in low structure and located in southeast of Cepu high, and the fault is as boundary between Cepu high and low structure which is possibly as the pathway of hydrocarbon migration, with northwest direction.

Reefall Prupuh as stratigraphy trap model in these area is overlaid by shale facies transgressive system tract of Tuban Formation as caprock, and the total thickness from the surface to the top of Prupuh Formation is at least 3000 m consisting of Miocene to Holocene sediments.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia