The Relationship between Seismic Amplitude, Lithology and Hydrocarbons in Southern RIP Block, Gulf of Thailand

Abstract

The variation of seismic amplitude with offset in the gas fields of the southern RIP block is the key to detecting gas reservoirs. This research analysed well log data in an attempt to interpret relationship between rock properties and acoustic impedance and to construct AVO models. The objective was to study sand properties and predict potential AVO classification. Well log data from the CB05S, PK11 and PM08 wells suggest that sands in this area are low impedance and can be separated from the shale trend. HampsonRussell AVO modelling was applied to synthetic seismograms using Aki-Richards equation to study amplitude variations with offset in term of interception and gradient relationship at top sands. The potential AVO responses showed low impedance sands in class III and IV. The angle stack seismic data was used to study seismic amplitude variation with offset in Near versus Mid stack seismic crossplots. Top gas and brine sand picks are negative amplitude in Near and Mid stacks (quadrant III) but cannot separate gas from wet sands. Base sands are quadrant I. This top sand crossplot was employed to detect sands in stacked seismic volumes and is useful tool for displaying lateral extent of sand body. Analysis failed to link seismic amplitude observations to AVO modelling because of the combined effects of seismic related issues, fault plane interference and pore fluid type uncertainty of sand. Seismic data have limited vertical resolution in this thin-bedded sand environment and seismic processing operations during stack affect accurate AVO analysis.