The controls of geomorphology and sediment supply on sequence stratigraphic architecture and sediment partitioning of the lacustrine rift basin in the Es₃ of Liuzan area, Nanpu Sag, Bohai Bay Basin, China

ABSTRACT

An important hydrocarbon reservoir is hosted by the third member of the Shahejie Formation (Es₃) in the Liuzan area, Nanpu Sag, Bohai Bay Basin, China. The Es₃ can be divided into five third-order sequences (from base to top: Sq1, Sq2, Sq3, Sq4 and Sq5). Utilising well logs, cores and high-resolution 3-D seismic data, this study investigates the development characteristics and styles of sediment transport pathways in the steep-slope zone of the lacustrine rift basin. Two styles of sediment transport pathway are identified in the study area, including the faulted trough and fault slope-break zone. The faulted trough is divided into a single faulted trough, synthetic faulted trough and antithetic faulted trough. The fault slope-break zone is composed of synthetic fault slope-break zone and antithetic fault slope-break zone. The fan-delta plain and fan-delta front are recognised in the study area. The different styles of delivery conduits control depositional facies types and the spatial and temporal evolution of fan-delta depositional systems from Sq3 to Sq5. Based on paleo-geomorphological reconstruction, the dispersal pattern of the steep-slope zone system divided into a northern steep-slope system and an eastern steep-slope system is established. In Sq3, the northern steep-slope system develops large-scale mixed sandy–muddy fan-delta deposits derived from the NW. The eastern steep-slope system feeds the medium-scale gravel-rich fan-delta sediments. In Sq4, the large-scale mixed sandy–muddy fan-delta deposits develop from the NNE direction in the northern steep-slope system. The small-scale sand-rich fan-delta sediments are transported from the eastern steep-slope system. In Sq5, the large-scale mixed sand–mud fan-delta deposits are fed by both the northern steep-slope system and eastern steep-slope system. The strata stacking pattern exhibits a seesaw mode in the study area. Based on the analysis of the channel-belt thickness and the fan-scales, the paleogeomorphology of the drainage area in Sq3 and Sq4 and sediment supply in Sq5 alternatively control the sequence stratigraphic architecture and sediment partitioning in the sink area. The model proposed in this study may aid in the prediction of favourable reservoirs and good source–reservoir–seal development in lacustrine rift basin.

KEYWORDS:

• sediment transport pathway
• paleogeomorphology
• sediment supply
• sediment partition
• sequence stratigraphic architecture
• Es₃
• Nanpu Sag

Acknowledgements

This study was supported by PetroChina Jidong Oilfield Company (2015-JS-185) and National Nature Science Foundation of China program (No. 41672100). We are grateful to the anonymous reviewers and Keyu Liu, the associate editor of Australian Journal of Earth Sciences, for their insightful reviews and constructive suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary papers

Table A1. Lower channel-belt and bankfull thickness measured from well logs in the study area.

Additional information

Funding

This work was supported by the National Nature Science Foudation of China [grant number 41672100].