Shelf break zone identification and its control on sedimentary sequence formations

On basis of previous studies, Zhujiang-HanJiang formtations in the shelf break zone in Panyu low-uplift and the north slope of Baiyun Sag of Pearl River Mouth Basin are considered as a sequence stratigraphic framework. Using drilling, logging and seismic data and sequence stratigraphic principle, the paper analyzes characteristics of sedimentary sequence system tract for SQhj2 of the middle segment of Hanjiang formation. The main observations are as follows: (1)SQhj2 can be divided into low-stand system tract, transgressive system tract and high-stand system tact. And the low-stand system tract can be recognized as two stages. (2)Based on incised channels on system tract, time isopaches and cross-well sections, the boundary of the shelf break zone of the SQhj2 located in the southeast of Well area C, is distributed in the near northeast direction. The fracture slope break zone is an important controlling factor of the depositional sequence formation of the SQhj2. (3)The shelf break zone and the low-stand system tract of the SQhj2 are well-developed favorable sand body area. Up-dip sand bodies overlay onto the sequence boundary or unconformity surface, and contact with the muddy layers of high-stand system tract and the upper slope. They are capped by overlying transgressive mudstone with a good sealing condition. So the onlap unconformity traps can be formed. Two-stage low-stand fans under the shelf break zone and the deep sea mudstone can form better reservoir-seal assemblage and favorable stratigraphic traps.