Petroleum reservoir potential of Pacitan subvolcanic rocks based on qualitative and quantitative analyses of porosity permeability

摘要

Pacitan Regency is the westernmost district of the province of East Java which is directly adjacent to 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 characterized by semicircular valleys flanked by hills in the east, north, and west. The hills are dominated by rocks of ancient Oligo- Miocene volcanic products known as the Old Andesite Formation. Pacitan stratigraphy, from the older to the younger, consists of Oligocene Volcanics (Mandalika, Watupatok, and Arjosari Formations), Early Miocene Carbonates (Campurdarat and Jaten Formations), Middle Miocene Volcanics (Wuni Formation), Late Miocene-Pliocene Carbonates (Nampol, Oyo, and Wonosari Formations), and Holocene alluvial deposits (Kalipucang Formation). The presence of dominant volcanic rock has been considered as an area without petroleum play prospect. To test this consideration, we study the potential possibility of petroleum system of southern mountainous sub-volcanic deposits which is commonly found in the Pacitan area. Jaten and the Nampol Formations are the interesting formations in terms of petroleum system because they are composed of sandstone, shale, and coal intercalations that are very rich in carbon materials. They also have the potential to be a reservoir because of their physical properties such as good porosity and permeability. This study is purposed to analyze the reservoir potential of sub-volcanic formation on the basis of their porosity and permeability properties. This study using petrographic thin section analysis and lab tests as the method.