Application of Spectral Decomposition and Seismic Attributes to Understand the Structure and Distribution of Sand Reservoirs within Tertiary Rift Basins of Gulf of Thailand

The Gulf of Thailand lies on the southern margin of the Eurasian Plate and contains a number of north-south trending Tertiary aged rift basins. These basins form a series of en echelon grabens and half graben systems. Significant graben shifts because of transfer zones between the early rift structures are expected in the area, but on conventional seismic no such discontinuities can be observed. The main reservoirs of the area are Lower to Middle Miocene sands associated with fluvial depositional systems. The facies distribution pattern of these reservoirs are of limited scale showing rapid lateral and vertical changes, which is not easy to resolve on conventional seismic data. The objective of the present study is to develop geophysical workflows to better image the faults and reservoir sand distribution in the area. We applied spectral decomposition (Discrete Fourier Transform) techniques, semblance and sweetness on a seismic data set from the Pattani Basin and on selected frequency slices observed NW-SE discontinuities which were additional to the N-S faults interpreted using conventional full spectrum seismic data. Iso-frequency volumes for phase and amplitude were also calculated. Key horizon slices of different phase volumes were examined and it was found that the 30 Hz phase volume best resolved both sets of faults (N-S & NW-SE). We also observed the same set of faults on horizon slices of semblance. Channels were identified on 25~30 Hz amplitude volumes within less tectonically disturbed zones. The good match between sweetness and gamma ray at well location indicates that we can use sweetness for sand prediction. Combining the results of amplitude volumes and sweetness, two types of channels can be identified: 1) those having high sweetness and high amplitudes at selected frequencies (25~30) and 2) those with low sweetness and low amplitude at selected frequencies which were associated with point bars of high sweetness and high amplitudes. We interpreted these types of channels as sand filled and mud filled associated with sandy point bars respectively. Both sets of faults also affect the anomalies associated with sand bodies. The present study reveals that spectral decomposition techniques combined with semblance and sweetness can successfully delineate sand geometries within the complex tectonics and depositional environments in the Gulf of Thailand.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California