| Taking the banded sand bodies developed in the mudstone of the Miocene Zhujiang Formation in the south of Huizhou Sag of the Pearl River Mouth Basin as the research object, the characteristics, genesis and control factors of the sand bodies are studied by comprehensive utilization of core, logging, seismic and production data. The sandstones are constituted of coarse grains, with excellent reservoir quality. The sandstones exhibit box or funnel-shape in GR curves, and show strong amplitude in seismic profile. In seismic amplitude map, the sand bodies extend as narrow and long strips in NNE, parallel with paleo-shoreline. These sandstones are forced-regressive shoreface deposits in falling stage system tract. The top and bottom of the sandstones are in abrupt contact with the mudstone of the continental shelf. The abrupt bottom is a within-trend forced regressive surface with high diachroneity. The abrupt top is sequence boundary, which corresponds to the lowest point of base level cycle. The top is eroded and transformed by following transgressive wave-ravinement, which is also flooding surface with low diachroneity. Long-term obliquity cycles influence the base level fluctuation significantly. When obliquity value is low, the global eustasy drops, and forced regression is triggered in Pearl River Mouth Basin. At this time, the sand bodies extend from the shore to the shelf, even to the carbonate platform. The forced regressive sandstones are important oil and gas reservoirs and migration channels, and they are also easy to form lithologic traps, which are important targets of oil and gas exploration. |
