Fluvial Reservoir Architecture from Near-Surface 3D Seismic Data, Block B8/32, Gulf of Thailand

Samorn, Hathaiporn¹ (1) Chevron Thailand, Bangkok, Thailand

This study aims to document the distribution and internal architecture of fluvial sand bodies using 3D seismic data from the Gulf of Thailand. Results were acquired from seismic time slices at a spacing of 4 msec in a shallow interval from 104-272 msec. High-resolution time slices and cross sections through the seismic data clearly image the architecture of valley systems within the Pleistocene to Holocene section. There is nearly complete preservation of alluvial depositional elements, including incised valleys, alluvial terraces, channels, neck cutoffs, and point-bars with meander scrolls.

Multiple channel systems are imaged. Compiled measurements from each channel include channel width, channel-belt width, cumulative length along each channel, channel length, half-meander wavelength, amplitude, asymmetry, azimuth, sinuosity, point-bar sizes and volumes, channel gradient, thickness of each channel, width/thickness aspect ratio, and paleocurrent direction.

The most clearly defined evidence for incised valleys is the presence of small tributaries. Also, incised valleys tend to be deep and wide systems that cut across older seismic reflectors. Six sequence boundaries are interpreted in this study interval, based on the presence of six levels of incised valleys. Channels that are not tributaries to incised valleys or incised valleys, are classified as unincised fluvial channels. These channels do not have tributaries. They are also smaller in size, and it is hard to see point bars and other internal architecture within the seismic data. They are imaged in only a few successive slices, as their thicknesses are significantly less than the incised-valley systems.