<![CDATA[The Miocene carbonate buildup and fine-grained clastic sequence become the main reservoir and sealing intervals in the East Natuna Basin. In this geological context, the reservoir characterization of Terumbu and Arang formation was conducted using an integrated methodology that includes petrophysical interpretation, followed by sensitivity analysis, structure depth mapping, and model-based seismic inversion. Well-log analysis reveals distinct lithological contrasts among the two formations. The Terumbu carbonates exhibit very low gamma-ray values (18 24 API) and high porosity ranging by 28 37%, locally reaching 31% in the GANG-4 well. Pronounced neutron density crossovers indicate gas-bearing intervals, particularly at depths of 6,808 6,831 ft and 6,908 6,941 ft in the GADO-3 well, where deep resistivity values increase significantly (852 1958 Ω·m). In contrast, the Arang Formation is characterized by high gamma-ray values (102 148 API), elevated clay volume (30 44%), and substantially lower porosity (<10%). P-impedance density cross-plots show carbonate clusters inside of impedance values of 4,500 10,000 g/cc·m/s and density ranges of 1.7 2.35 g/cc, whereas shale and shaly sand plot at higher impedance (9000 17,500 g/cc·m/s) and density (2.45 2.80 g/cc). Depth structure mapping identifies a central northern structural high that favors reef development and fault-controlled trapping. Model-based seismic inversion reveals low to medium impedance values (4100 6156 g/cc·m/s), low density (1.57 1.77 g/cc), and high inverted porosity (0.37 0.52, locally up to 0.70) Inside the top Terumbu interval, indicating very good quality of reservoir rock is confirmed by these outcomes. Conversely, the underlying Arang interval becomes tighter and denser by a continued increase in impedance ( by porosity values <11%) and poor reservoir potential.]]>
