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Fluvial systems in the Gulf of Thailand – Stratigraphic Implications for Exploration and Development

Abstract

The Miocene section of the Gulf of Thailand is dominated by fluvial deposits, which comprise the principal productive play. The fluvial systems are characterized predominantly by moderate to high sinuosity, with single-threaded systems with side-attached bars. Within the shallow-buried Pleistocene part of the subsurface, analogous deposits are observed from which detailed metrics can be extracted. Seismic stratigraphic and seismic geomorphologic analyses reveal a wealth of detail within these deposits. Vertical resolution within this part of the 3D seismic volume is ∼5.7m. However, although below resolution, significant features nonetheless can be detected down to ∼1.4m inasmuch as this comprises the limit of detectability. In addition to the regional 3D seismic, geohazard sparker seismic data were also available in a loose 2D grid of seismic sections. These 2D data complement the 3D seismic data and provide a much higher level of resolution of ∼ 25cm. Integration of the 2D and 3D seismic data sets allows for detailed measurements of both stratigraphy and geomorphology. Four parameters were measured for multiple fluvial systems: river (i.e. channel) width, point bar thickness, channel wavelength, and channel sinuosity. Excellent correlations exist between channel wavelength, river width, and point bar thickness. Channel sinuosity, however, did not correlate well with the other parameters, highlighting the difficulty in predicting sinuosity on the basis of point bar thickness or river size. Channel wavelength scaled to ∼30.2 times the channel (i.e. river) width. Channel wavelength scaled to ∼514 times the point bar thickness. And channel width scaled to ∼17 times the point bar thickness. In each of these latter instances, the statistical significance was to the 0.01 level. Based on these metrics, point bar thicknesses can be predicted based on channel widths observed on 3D seismic plan view images. Likewise, point bar thickness can be estimated based on observations of channel wavelength observed on 3D seismic plan view images. Alternatively, if point bar thickness is known through borehole observations, then channel wavelength can be estimated, which can yield rough estimates of point bar size.