SEISMIC FACIES ANALYSIS OF OLIGO-MIOCENE REEF IN RAMA FIELD, ONSHORE EAST JAVA BASIN: IMPACT OF FLUCTUATING RELATIVE SEA-LEVEL CHANGE TO FACIES DEVELOPMENT

摘要

Rama Field is considered as one of mature hydrocarbon fields in Northeast Java Basin, comprising Oligo-Miocene carbonates of Kujung Formation. Based on production history, it reveals that the reservoir interval has not yet reaching its maximum performance due to complexity of carbonate facies. This study was intended to obtain better understanding of reef facies and other facies within the stratigraphic framework in Rama Field, as well as to help optimize the potential of reservoir facies within this area. 3-D seismic data of the Oligo-Miocene section within Rama Field is generally characterized by high amplitude, mound shaped structure and absent internal-reflections, a particular feature which showed as reef geometry. Development of the reef facies and other facies were initiated during highstand building the carbonate reef and keeping up with relative changes in sea-level. Toplap and onlap terminations indicates deposition during lowstand condition, forms the Sequence Boundary (SB). During this time, reef development was terminated, and thus interpreted as give-up phase. Final phase is characterized by rapid transgressive, resulting in development of reef-facies, pre- dominantly composed of boundstone, packstone and wackestone. Moreover, core analysis reveals that this facies is considered as the best candidate for reservoir, including 2.2 - 33.1 % of porosity and 0.01 - 2516 mD of permeability ranges. Together, this evaluation provides better understanding of carbonate facies characteristic and their potential as petroleum resevoir utilizing integration method and interpretation. Accordingly, the interpretation of carbonate facies within chronostratigraphic framework is very important for oil and gas field development.