The Shelf-margin Delta Feature and Its Significance in Zhuhai Formation of Deep-water Area, Pearl River Mouth Basin

Key words: 
• shelf-margin delta /
• main control factors /
• Zhuhai Formation /
• Deep-water area in Pearl River Mouth Basin

Abstract: A shelf-margin delta is built up on shelf-margin, where sediments pass across the shelf break and settle down to form the delta. Oil richness of shelf-margin delta has been confirmed by exploration in the world for its wide distribution and well-developed reservoirs. Based on analysis of seismic and drilling data, distribution and architecture of large shelf-margin delta in Zhuhai Formation in deep-water area have been systematically studied for the first time, as well as the main control factors and exploration significance. With “S”, oblique and imbricated progradation configuration in profile, interbedding of underwater distributary channel, mouth bar, sand sheet and prodelta clay on wells, the large shelf-margin delta striking NE is located in Baiyun and Heshan sag. In Baiyun sag, this delta is relatively small with mainly oblique progradation configuration. The delta in South Baiyun depression developed deepwater channel and fans with “S” progradation configuration. The segment in southern uplift show oblique and imbricated progradation configuration. In Heshan sag, the delta developed incised valley and fans with “S” progradation configuration. Shelf break developed firmly in deepwater area for quiescence of tectonic movement in Late Oligocene. Shelf-margin delta developed because of the abundant sediment from Paleo-Pearl River and falling of relative sea-level. The delta takes abundant terrestrial organic matter to marine mudstone and, moreover, mudstone in the delta is fair-good source rock. With wide distribution and big thickness, underwater distributary channel, mouth bar and sand sheet in shelf-margin delta are significant reservoir in deepwater area and the deepwater fans before delta are profitable target.