Sedimentary characteristics and evolution of the fluvial system of the Neogene Guantao Formation, Zhanhua Sag, Bohai Bay Basin, China

Abstract

Fluvial facies sand bodies are important reservoirs for oil and gas resources. In this study, the sedimentary characteristics and evolutionary patterns of braided and meandering fluvial deposits in the Neogene Guantao Formation of the Zhanhua Sag, Bohai Bay Basin were analyzed using cores, well logs and three-dimensional seismic data, and the quantitative information of the sand bodies in different fluvial deposits were characterized with dense well-net constraints. Through the calibration between the core and wireline logging data, the developmental characteristics of the sand bodies in the braided and meandering deposits were clearly defined base on single-well sedimentary microfacies interpretation templates. Composite fluvial channel sand body facies associations develop in braided fluvial or high-sinuosity meandering fluvial deposit, and single fluvial channel sand body facies associations develop in a mid-sinuosity meandering fluvial deposit. The fluvial sedimentary evolutionary model was established based on the reconstruction of sedimentary characteristics. Factors such as the relative sea or lake level, climate, and tectonics control the change of the river. During the late period of Guantao Formation deposition, the tectonic movement tended to be stable; thus, climate change was the most important factor in the fluvial style change and the lake level rise also showed an influence. There is a positive correlation between the width and thickness of the braided fluvial channels and the mid-sinuosity meandering fluvial channels; however, this is relatively poor for the high-sinuosity meandering fluvial channels.