Seismic Geomorphology of the Lobed-Channel System of Upper Miocene Huangliu Formation, Yinggehai Basin, Northwestern South China Sea

Abstract

Three-dimensional seismic data have been widely used in interpreting ancient river systems and their associated sediment deposits. Thin-bed reservoirs of lobed-channel system in lithostratigraphic units of Dongfang (DF) area are one of the major study areas for reservoir growth in the Yinggehai basin of northwestern South China Sea. Although it is understood that the transport mechanics of parent substrate and alluvium determine the morphology of channel for lobed-channel system, the transport mechanism and regional gradient are relatively poorly understood. This study is focused on the application of various techniques in seismic geomorphology to the Yinggehai Basin to assess influences of regional gradient and relative sea level change on lobed-channel morphology. The Blue River delta received material from the western Vietnam Blue Rriver drainage system during Paleogene to Neogene. The gravity flow system in the DF areas has a close genetic relationship with the Blue River delta. In 3-D seismic survey area, four fifth-order sequences in first member of upper Miocene Huangliu formation were identified using well and seismic data. Seismic inversion and 90° phasing of seismic data were used to convert seismic traces to pseudolithologic logs. Stratal slicing made it possible to interpolate and extrapolate well-data-derived sequence and identify submarine fan, channel fill, lobes and overbank deposit. Strata slices suggested that sea-floor slopes exerted main influence on channel morphology. Specifically, DF13-1 block had high gradient, which mainly distributed mud-sand-rich lobes. However, DF13-2 block established low gradient, which mostly indicated sand-rich braided channels. The values of sinuosity, channel widths, meander-belt widths in DF13-2 block are all greater than these in DF13-1 block. In addition, results of carbon isotope measurements and foraminiferal research of two blocks suggest that paleo sea level in DF13-2 block was higher than that of DF13-1 block. It also deciphered why channels in DF13-2 incised deeply because of the stronger hydrodynamic energy. Thus DF13-2 block was formed in a lobed-channel and sand rich system, compared with DF13-1 of channelized-lobes and mud-sand rich system.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016