Revisitting Cisubuh Formation in Onshore North West Java Basin; New Analysis from Seismic Stratigraphy, Geochemistry, and Subsurface Perspective; Implication for Petroleum System and Shallow Target Hydrocarbon Exploration in Northwest Java Basin;Case Study Randegan Field and Mt. Kromong Area

Abstract

Onshore Northwest Java Basin (NWJB) is one of the proven hydrocarbon basin in Indonesia. Conventional Play for this basin are limited to deep reservoir target such as Parigi, Cibulakan, BRF, TAF and Jatibarang Formation. This lead to high cost for drilling. This Paper present new insight on Shallow target with less than 1000 m and proven as good reservoir. Previous study show that Cisubuh Formation is not a reservoir in many regional stratigraphy chart; it is a regional seal in onshore NWJB. This Formation contain only shale with intercalated sandstone in previous study. The method in this study is detail subsurface mapping of Cisubuh Formation in onshore NWJB including Seismic inversion analysis from seismic data to detect hydrocarbon anomaly, combine with lithological description from cutting and integrated with outcrop data and geochemistry data. Sequence stratigraphy and lithological description is use to make more accurate stratigraphic colomn of Cisubuh Formation. The result show there are Carbonat buildup in Cisubuh Formation, transgressive sand that have good reservoir property and conglomerate. Moreover, from outcrop study it show that Total Organic Carbon from 17 sample have a value 0,27 - 4,43%, it means Cisubuh Formation have a low-very good candidate as a source rock. From Pirolysis Rock Eval Analysis show that this formation have Tmax 331-557° C with Hydrogen Index 3-338 H/g. That means that the sample from this Formation is mature-over mature and from Hydrocarbon index this formation categorized as gas prone and oil prone. Drilling of KYM-01 well proving that Cisubuh formation is a good reservoir, it produce two MMSCF gas from Cisubuh interval. Optimizing this sudy will help for future development on many oil fields on onshore NWJB, shifting the paradigm from depth reservoir target