Reservoir characteristics of the weathered crust in the paleo-buried hill of Baoyunting structural, Xihu Sag, East China Sea

The slope belt of Xihu Sag is a key exploration area in East China Sea Shelf Basin.Its deep-buried weathered crusts in the paleo-buried hills draw significant attention. However, unclear distribution patterns of reservoir units in these weathered crusts severely restrict the exploration progress. Based on the regional tectonic background, through core observations, thin-section analysis, this paper studies the characteristics of the weathered crust reservoir in Baoyunting structual of Xihu Sag. The results show that the shallow weathered crust reservoir of buried hills can be vertically divided into residual clay zone, residual sand-gravel weathering zone, while deep bed-rock reservoir can be divided into top fracture zone and deep fracture zone. The types of reservoir spaces are orderly non-porous, pore-fracture type, fracture-pore type, and fracture-dominated type. Main controlling factors for reservoir development include weathering-leaching processes, cooling joints, tectonic activities, and magmatic activities. The reservoir development model reveals that the residual sand-gravel weathering zone within the weathering crust is the most favorable exploration target, which provides critical geological insights for optimizing hydrocarbon exploration strategies in deep paleo-buried hill systems.