Publications

The Gulf of Thailand lies on the southern margin of the Eurasian Plate and contains a number of northsouth trending Tertiary rift basins. These basins form a series of en-echelon grabens and half-graben systems. The main reservoirs of the area are Lower to Middle Miocene sands associated with fluvial depositional systems. These reservoir sands are compartmentalized and show rapid lateral stratigraphic changes due to their fluvial nature. Moreover, these reservoir sands are further segmented by intra-basin faults influenced by preexisting basement fabrics. Rock physics and seismic inversion techniques were applied to map the distribution of reservoir sands and to study the depositional style related to tectonics within the Miocene interval of one of the basins of the Gulf of Thailand. Rock physics analysis shows that variation in PImpedance can only differentiate high porosity sands (total porosity > 22-24%) from shale while lower porosity sands have similar P-Impedance to shales. However, relatively lower porosity sands (total porosity up to 18-22%) can be detected by using P-Impedance and Vp/Vs information in combination. A P-Impedance volume was computed through post-stack seismic inversion and the results are in reasonable match with the P- Impedance logs at well locations for high porosity sands. As well, pre-stack simultaneous inversion was performed to compute P-Impedance and Vp/Vs volumes. The results were checked by different QC parameters. Sand bodies were delineated using computed thresholds of P-Impedance and Vp/Vs volumes based on a correlation to well data Most of the sand distribution is restricted to the faulted zone which forms the western boundary of the basin. It appears that sedimentation was controlled by the dominant N-S structural configuration of the basin and * Chulalongkorn University /Currently at Statoil Indonesia ** Chulalongkorn University occurred in response to rifting evolution in the Miocene. The sand bodies interpreted using the post-stack and pre-stack inversion data volumes indicate that intra-basin faults also break the sand connectivity. This study reveals that seismic inversion techniques can successfully map reservoir sand distribution within the rift basins in the Gulf of Thailand.