Central Java was one of the rich area in Indonesia where oilseeps found between volcanic deposits. One of the oilseeps appeared in North Serayu Mountain near Serayu River upstream, South Serayu area. The research area was located at Banyumas regency, Central Java extend between 109o 13’ 30’’ – 109o 18’ 30’’ East Longitude and 7o 28’ 30’’ – 7o 33’ 30’’ South Latitude. In Paleogene ( Eocene – Oligocene ) volcanic arc in southern java developed a basin called Banyumas basin. In Oligocene – Miocene, Banyumas Basin was an intra arc basin which dominated by volcanic clastic rocks. The changing process from intra-arc basin to fore-arc basin caused by magmatic volcanic arc which moved to the north direction. Volcanic of Java moved to the northern side in Neogene because trusting angle of oceanic crust behind java was lower than the angle in Paleogene. Mid Miocene – Late Miocene reservoir target in Banyumas was still prospective but a lot of mechanical trouble in old wells or Jati-1. Then, one of several problems is hard to do the seismic interpretation. It caused by the characteristic of rocks in Banyumas Sub Basin which consist of thick volcaniclastic sediments. Besides, North East – South East Pamanukan – Cilacap Fault Zone caused a subsidence in Banyumas Sub-Basin basement in Mid-Miocene. In Upper-Miocene, there was an uplift occurred in Halang Formation which made Banyumas Sub- Basin became “deeper”. Lateral faults in deep horizons also made a determination of reservoir became harder than reservoir influenced by vertical faults that commonly in Indonesia. The existing of limestone in Kalipucang Formation as a source rock was possible based on TOC value from geochemistry analysis. Early Miocene Kalipucang Formation which influenced by subsidence in Banyumas Sub- Basin basement. In this situation, geothermal gradient have a possibility to maturate the source rock. Furthermore, hydrocarbon accumulation took place in Halang Formation. This paper will examine and describe in detail the influence of tectonic activities and sedimentary processes, opportunities and risks that happened in Banyumas Sub-Basin.
Author : R. A. Wicaksono, Syahreza S. Angkasa, Fariza F. Azmalni, Andika D. Kahfi, Alfardi A. P