Abstract

Recently, the rift-related successions in the Eocene Huizhou (HZ) Depression have been considered crucial intervals for hydrocarbon exploration in the Pearl River Mouth Basin, China. However, the facies delineation and sandstone distribution are poorly understood due to the limited well data. Our study area is the HZ25 Block in the HZ Depression, which consists of a typical overlapped synthetic transfer zone connecting the HZ26 and XJ30 Sags. Integrated analysis of seismic and logging data indicates that the Eocene Wenchang Formation can be subdivided into four third-order sequences (SQ1–4). Well-based observations reveal that the braided deltaic system is mainly characterized by distributary channels, subaqueous distributary channels, mouth bars, and sheet-sand deposits. The sandstone isopach map acquired by seismic inversion indicates that the sandstone could be 340 m thick in the SQ2 but sharply decreases in the SQ3 in the transfer zone area. Stratal slices make it possible to delineate the facies maps by extrapolating the well observations to the entire 3D seismic survey; it is suggested that the SQ2 deltaic package largely comprises braided delta plain (distributary channels) and front deposits (subaqueous distributary channels and mouth bar) with a broad distribution of 50  km2, whereas the SQ3 deltaic package is dominated by delta-front deposits only 20  km2 in extent. This study suggests that small-scale fan-delta deposits are confined to the central part of the boundary fault, whereas the transfer zone captures large-scale braided delta sediments with a long transportation distance up to 8 km. The sandstones developed in the northwestern part of the transfer zone within the SQ2 sequence are expected to form potential hydrocarbon reservoirs for future oil exploration. Furthermore, this study may have implications for reservoir prediction and hydrocarbon exploration in other areas lacking well data, such as the HZ Depression.

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