SOURCE ROCK AND RESERVOAR POTENTIAL OF SUB-VOLCANIC BASIN STUDYCASE: JATEN FORMATION AND NAMPOL FORMATION, PACITAN, EAST JAVA
C Prasetyadi (*), M Gazali Rachman (*), Achmad Subandrio (*), Mahap Maha (*)
(*) Geological Engineering Department, UPN "Veteran" Yogyakarta
Abstract
Pacitan Regency is the easternmost district of the province of East Java which is directly adjacent with the Wonogiri Regency (Central Java) to the west. Pacitan can be reached in about 4 hours from Yogyakarta by land transportation via the southern route of Java. The morphology of the pacitan district is very unique. Pacitan city is a semicircular valley flanked by high hills in the east, north, and west. The hills are dominated by rocks of ancient Oligo-Miocene volcanic products commonly called the Old Andesite Formation. Pacitan stratigraphy according to Samodra, et al (1992) from the oldest to the youngest are Oligocene Volcanic (Mandalika Formation, Watupatok Formation, and Arjosari Formation), Early Miocene Carbonate (Campurdarat Formation, Jaten Formation), Middle Miocene Volcanic (Wuni Formation), Late-pliocene miocene carbonate (Nampol Formation, Oyo Formation, Wonosari Formation), and holocene alluvial deposits (kalipucang Formation). Pacitan district is not an oil and gas producing district like other districts in North East Java because the presence of dominant volcanic rocks is not considered to be a prospect petroleum play. For this reason, we need to study the potential of the petroleum system of southern mountainous sub-volcanic deposits. This study started from Pacitan district. Jaten Formation and the Nampol Formation are interesting formations in terms of petroleum systems because they are composed of sandstone, shale, and coal intercalations that are very rich in carbon materials. In the other hand they also have the potential to be a reservoir because their physical properties such good porosity and permeability. This study uses surface data with detailed stratigraphic cross section measurements, Rock Eval Pyrolysis (REP), Reflectance of Vitrinite and Kerogen Type of selected samples to analyze the potential of Jaten and Nampol formations to become a source rock. In addition, porosity and permeability analysis was also performed using petrographic thin section analysis and lab tests.
Keywords: Pacitan, Petroleum, Reservoar, Source Rock, Jaten
Topic: Geology