Theory of petroleum geology at 10 000-meter depth: Challenges of hydrocarbon exploration depth limits and resource potential

The successful drilling of well Shendi Take-1 has opened a new era in the petroleum industry, marking the beginning of 10000-meter deep hydrocarbon exploration. Consequently, investigating the hydrocarbon exploration depth to its limits and the boundaries for hydrocarbon occurrence has become a hot topic in the geological community. In this study, we present a systematic summary of the discoveries and geological theory of hydrocarbon exploration at a depth of 10000 m. The hydrocarbon generation potential of the Nanhua, Ediacaran, and Cambrian source rocks is quantitatively assessed. It is demonstrated that the depth threshold for preserving liquid oil extends up to 9000 m in basins with low geothermal gradients, thereby enhancing the potential for ultra-deep oil exploration. Mechanisms responsible for the preservation of large-scale oil reservoirs formed 250 million years ago are identified, supporting the exploration of ultra-deep ancient hydrocarbon reservoirs. Furthermore, it is proposed that carbonate reservoirs exhibit no definitive lower depth limit. Additionally, a new type of fractured-vuggy oil reservoirs, formed by complex seepage processes and characterized by multiple oil-water interfaces, is identified. This discovery reveals the mechanisms by which secondary geochemical processes modify the properties and phases of hydrocarbons. Ultra-high oil and gas columns are discovered in ultra-deep reservoirs, revealing the enrichment and distribution patterns of hydrocarbons in high-yield and high-efficiency wells. These findings provide theoretical support for achieving major hydrocarbon discoveries in ultra-deep reservoirs and for reshaping hydrocarbon exploration strategies. Furthermore, they also open the new frontier of hydrocarbon exploration at a depth of 10000 m, marking a new era for the petroleum industry. Additionally, we analyze major challenges in the geological theory of hydrocarbon exploration at such a depth, propose the concept of limit hydrocarbon exploration depth, and examine the boundaries for hydrocarbon occurrence. It is therefore essential to accelerate efforts to bridge the knowledge gap created by the high temperature and high pressure conditions in the Earth's interior, thereby enabling free hydrocarbon exploration within the limit depth range. Such progress will help position hydrocarbon resources in 10000-m-deep plays as a vital component in safeguarding China's energy security.