Application of spectral decomposition and seismic attributes to understand the structure and distribution of sand reservoirs within Tertiary rift basins of the Gulf of Thailand

Abstract

The Tertiary rift basins in the Gulf of Thailand are the major hydrocarbon producing areas of Thailand. The reservoirs in these basins are predominantly Lower to Middle Miocene fluvial channels and overbank sands and these reservoirs are segmented due to post-depositional faulting (Racey, 2011). There are small closely spaced sealing faults, which compartmentalize the sand reservoirs and are not easy to map on conventional full spectrum seismic data. This fault system is oblique to the regional north-south extensional fault system and is related to graben shifts/transfer zones associated with changes in dip of graben provinces and zig-zag map pattern of the regional north-south faults (Kornsawan and Morley, 2002). Most wells until now have been drilled on structures along the faults and it is common to encounter different sand facies with different fluid contents in closely spaced wells at the same depth intervals. Because of these structural and stratigraphic complexities, it is required to develop geophysical workflows to better image faults related with graben shifts and map the reservoir sands in the area. In this study, we analyzed a 3D seismic data set over a gas field in the Pattani Basin (Figure 1) where we applied a spectral decomposition technique to resolve these exploration issues. Moreover, semblance and sweetness attributes were also calculated to assist in the fault and sand detection, respectively.