The deep subsag areas of lacustrine basin exhibit significant potential for both conventional and unconventional hydrocarbon exploration

yet challenges persist in unclear understanding of hydrocarbon accumulation mechanisms and undetermined exploration targets. Based on exploration practices in the deep subsag areas of Huanghua depression

as well as the comprehensive analysis results

of core samples of 1 100 meters and logging data

this study reveals orderly hydrocarbon accumulation in the Whole Petroleum System under the coupling effect of multiple factors including tectonic structure

source rock and reservoir in the deep subsag areas of Huanghua depression as below. (1)The subsag area has excellent source rock conditions

with total organic carbon content of 1.6 % to 3.4 % and the majority kerogen types of Ⅰ to Ⅱ

1

. (2)The sedimentary facies show stratified differentiation

corresponding to river delta sandstones in the outer circle

prodelta sandstone and mudstone interbeds in the middle circle

and deep-lacustrine shale in the inner circle. (3)The diagenetic process exhibits distinctive features

such as inhibited compaction under overpressure

and significantly enhanced porosity owing to organic acid dissolution. Research indicates that hydrocarbon migration and accumulation are under the dual control of source-reservoir coupling and dynamic differential driving

forming a continuous reservoir sequence of conventional oil and gas in the outer circle

tight oil and gas in the middle circle

and shale oil and gas in the inner circle. Exploration practices have confirmed that the main far-shore underwater fan channel in the Member 3 of Shahejie Formation in Qikou deep subsag

the braided delta front sands and high-frequency laminated shales in the Member 2 of Kongdian Formation in Changzhuang deep subsag are key targets for subsequent exploration. The orderly distribution pattern of conventional-unconventional petroleum resources in deep subsag areas has not only guided explorations to achieve great breakthroughs in the study area

but also provided a valuable reference for exploring similar deep subsag areas of lacustrine basin.