Pore Pressure Predict Using Eaton Method and Sensitive Elastic Property Seismic of Overpressure Anomaly, Study Case: Poseidon Field, Browse Basin

Abstract In the pre-development phase of oil and gas exploration, drilling new wells is crucial for maximizing hydrocarbon potential. In order to ensure safe drilling operations, it is necessary to study pore pressure for prevent kicks and, in the worst-case scenario, blowouts. The primary objective of pore pressure studies is to identify overpressure zones. This research utilizes open data from the Poseidon Field in the Browse Basin, Australia. Pore pressure estimation is conducted using sonic logs with the Eaton method, validated by mud weight data and Modular Dynamic Test (MDT) results. The Eaton method is determination by effective stress that is obtained by sonic data, hydrostatic pressure is assumed as gradient of 0.431 psi/ft, and overburden pressure that derived from density. Overpressure zones are indicated by pore pressure values that are higher than hydrostatic pressure and effective stress. Based on pore pressure calculations, top overpressure zone is identified in the Jamieson Formation. These findings are supported by rock property analysis, which reveals the accumulation of thick shale average at depths from 3500 to 3700 meters and hydrocarbon potential average at depths from 3700 to 4500 meters. Sensitivity analysis of elastic seismic properties, color-coded for pore pressure, is performed using cross-plot techniques. Analysis of Acoustic Impedance (AI) and Shear Impedance (SI) indicates that these parameters are sensitive to overpressure conditions. The cutoff value of the P-impedance parameter that overpressure occurs is below 9200 (m/s)*(gr/cc) and for S-impedance parameter, the cutoff value obtained is below 5400 (m/s)*(gr/cc). The overpressure anomaly manifests as low values in the elastic parameters of P-impedance and S-impedance. These characteristics arise because velocity is an effective function of stress. According to the Terzaghi equation, the increases of pore pressure is aligned with the decreases of effective stress, leading to the observed anomalies in the impedance values.