Carbonate Reservoir Characterization of the Peutu Formation Based on Acoustic Impedance Inversion Method at FA Field, North Sumatra Basin.

Abstract

This study analyzes the spatial distribution of P-impedance and porosity in the Peutu Formation, a carbonate build-up formed through multiple sedimentation stages. P-impedance volumes were derived from model-based seismic inversion. The results show that low P-impedance values (10,000–11,500 g/cm³·m/s) are concentrated in structurally higher areas and correlate with higher porosity values (12–16%), with the porosity distribution map obtained by applying a linear regression equation to the P-impedance volume. These zones are associated with lower compaction, which helps maintain higher porosity and better reservoir quality. In contrast, well FA-C-5, located in a deeper structural position, exhibits higher P-impedance values (12,900–13,400 g/cm³·m/s) and lower porosity (5–10%), indicating more intense compaction and diagenetic alteration, including lime mudstone crystallization, as supported by log data. This contrast between high P-impedance with low porosity and low P-impedance with high porosity shows how structural depth and diagenesis affect reservoir quality. The results confirm that model-based inversion effectively maps reservoir heterogeneity and supports better well placement.

Keywords: Peutu Formation; P-impedance; Porosity; Seismic inversion; Reservoir characterization.