Geochemical characteristics and source of crude oil in Xihu Sag, East China Sea Shelf Basin

The geochemical characteristics of oil in the Central Anticline, Santan Sag and Baochu Slope were determined, and the oil source correlation and the process of oil accumulation were analyzed based on geological and geochemical analyses. There are differences in crude oil maturity, parent material source and accumulation process in different tectonic zones. The crude oil in the Xihu Sag is distributed in the mature or high maturity range. The Central Anticline is dominated by mature crude oil, and that in the Santan Sag and Baochu Slope is in the mature or high maturity range. The oil source correlation results show that the crude oil in the Huagang Formation mainly sourced from the argillaceous source rocks in the Huagang Formation in the Central Anticline, and the argillaceous source rocks in the Pinghu and Huagang formations in the Santan Sag. The crude oil in the Pinghu Formation on the Baochu Slope mainly originated from the coal-series source rocks in the Pinghu Formation, while those in the Baoshi Formation mainly sourced from the argillaceous source rocks in the Baoshi Formation. The crude oil in the Xihu Sag generally has the accumulation mechanism of “evaporative fractionation and gas-washing fractionation”, and those on the Baochu Slope are the most typical.