Abstract

3D seismic data from a Tertiary basin in the Gulf of Thailand imaged a four-way dip closure containing an oil rim and an overlying gas cap. A crestal region of high seismic amplitudes was found to be segregated into two by an unexpected area of low amplitudes impinging on the crest and the eastern flank of the anticline. The low amplitudes could relate to a significant change in reservoir characteristics and might therefore lower the potential of the prospect. Seismic attribute analysis and recursive inversion modeling were performed to decipher geological details and to image the fluid contacts within this anticlinal closure. Data from three deviated wells were integrated with the 3D seismic data volume for the inversion.

Seismic amplitude and attribute extractions enabled imaging of hydrocarbon distributions, confirmed the fluvio-deltaic depositional environment, and characterized the reservoir of interest as a channel-associated, lobate deposit. Recursive inversion modeling indicated the area of low seismic amplitudes to be a region of relatively lower porosity and higher velocity, interpreted to represent an increase in the shale content of the sandstone reservoir. The extracted porosities slightly overestimate measured wireline porosities, and possible static shifts in the data over the area of investigation diminish confidence in the results.