Hydrocarbon accumulation process in the Structure Y of Xihu Sag, East China Sea Shelf Basin and its implications for feature exploration

In order to support the next cycle of hydrocarbon resource evaluation and decision making process for the structure Y in the East China Sea Shelf Basin so as to break the bottleneck of future exploration, the hydrocarbon accumulation process of the structure Y was studied by means of balanced sections, multi-index comprehensive correlation of oil and gas sources, fluid inclusions and basin simulation. Results show that the structure has suffered three stages of hydrocarbon accumulation since 23 Ma, which eventually leads to the largest accumulation of hydrocarbon in the lower part of the Huagang Formation. The upper part of the Middle Huagang Formation only has hydrocarbon accumulated while it passes by the structure, and the reservoirs above the Longjing Formation are small and occasionally filled by oil and gas. The compression framework, which is " strong in north and weak in south”, controls the overall distribution pattern which is " rich in north and poor in south”; the transverse tensional fault formed by the Longjing movement is the key to control the vertical distribution pattern of oil and gas in the sequence of the upper Huagang Formation and above. Paleo-reservoirs in the lower part of Huagang Formation formed during the first reservoir forming period are the favorable direction for finding new sweet spots.