MAPPING OF RESERVOIR SANDS USING SEISMIC ATTRIBUTES AND POST STACK SEISMIC INVERSION IN NAM CON SON BASIN OFFSHORE VIETNAM

Abstract

The study area lies within the Nam Con Son Basin located in East Sea offshore Vietnam. The reservoirs in the study area are Middle Miocene clastics of deep marine origin. The reservoirs are heterogeneously distributed and distribution of the reservoirs is further complicated due to complex extensional fault system. Therefore mapping of these reservoirs is difficult based on seismic data. The purpose of this study is to apply rock physic analysis, seismic attributes and post-stack seismic inversion to map sand geometries and hydrocarbon zones. According to rock physics analysis, P-impedance of shale is less than the sand, and the presence of gas within sand reduces the P-impedance. Therefore P-impedance of gas sands and wet sands is different. However, P-impedance of shale and gas sand may partially overlap within the larger interval. Hence, by the analyze P-impedance within the narrow zone of the reservoir we may successfully map the gas sands and differentiate gas sands and wet sands. The extracted P-impedance horizon slice along inverted P-impedance volume successfully mapped the gas sand distribution. RMS attribute shows high amplitude along gas saturation zone. Low-frequency amplitude anomalies obtained from spectral decomposition indicates high value at well with high gas percentage, whereas at the well with a low proportion of gas, it does not show high amplitude. Thus, the combination of spectral decomposition and seismic inversion may successfully map hydrocarbon distribution. The fault blocks which are close to the high structure has relatively more sand. The proposed workflow for mapping sand and gassand can be used forthe furtherwell drilling programs.