APPLICATION OF LITHO-SEISMIC CLASSIFICATION BASED ON SIMULTANEOUS INVERSION RESULTS TO DETECT OFFSHORE BARS: CASE STUDY - SISI MAIN ZONE, SISI-NUBI FIELD OFFSHORE MAHAKAM DELTA

摘要

Simultaneous seismic inversion was performed on the 3D PSDM data covering the Sisi Nubi field located offshore in the Mahakam PSC. The classification of litho-seismic facies was computed from the inverted P-impedance (IP) and Poisson’s Ratio (PR) cubes in order to predict the probabilities of various lithologies. The lithology probability cubes provide useful information to update geological models and to locate future wells. Each lithology has distinctive petrophysical properties that could be defined using log data (sonic and density) and predicted from prestack seismic inversion results (IP, or PR cubes). In the shallower zone (less than 3000 m TVDss), the cross plot of P-impedance (IP) and Poisson’s ratio (PR) shows not only a good separation among different lithologies such as sands, shale, and carbonates, but also between gas- and water-bearing sand reservoirs. However in the deeper interval of Sisi Main Zone (SMZ), the differentiation between gas- and water-sands is ambiguous especially due to the burial effects. Even though detecting the fluid contents is challenging in SMZ, the separation among different lithologies like sands, shale, and carbonates is still possible and this is important information for future well planning. The main objective of this project is to detect the extension of the offshore bars in the Sisi field Main zone interval by using pseudo Vclay volume calculated from the litho-seismic classification. A QC at blind wells was done to validate the results. This study has largely improved the uncertainties of the sand probability over SMZ, and shows a good correlation between sand probability values and sand thickness found at the wells. They have been directly applied to determine the targets for the future development wells.