Application of seismic post-stack inversion for gas reservoir delineation: A case study of Talang Akar Formation, South Sumatera Basin

Nauli Field is one of the marginal fields that is located in the western region of Indonesia and has been proven to produce oil and gas hydrocarbons. The field is located in the South Sumatra Basin with reservoir target is sandstone from Talang Akar Formation. The purpose of this study is to integrate petrophysical interpretation and seismic data analysis. Reservoir characterization was performed based on porosity and water saturation for each layer within the wells. Seismic inversion methods chosen to estimate the attributes of P-impedance (Zp), S-impedance (Zs) and density (ρ). Amplitude Versus Offset (AVO) inversion through Lambda-Mu-Rho (LMR) attribute can provide information on lithology and fluids content in the reservoirs. The connection between seismic inversion and AVO inversion was to validate the gas content from the seismic data and its lateral dispersion. Data processing and analysis shows that the effective porosity for Nauli Field is between 10 to 20 porosity unit (p.u) with 20-70% water saturation. The thickness of net pay is 2-8 meters. Post-stack inversion shows impedance anomaly around 1580-1590 ms with value 22.000-25.000 (m/s)^∗(g/cc). Petrophysical analysis estimated this anomaly as layer-x sandstone with gas fluid saturated. LMR attribute confirm this fluid with lower Lambda-Rho values around 11-20 (Gpa)^∗(g/cc) than Lambda-Rho values around 28-32 (Gpa)^∗(g/cc).