China Discovers Seventh Billion-Ton Oil and Gas Field in the Bohai Sea

China National Offshore Oil Corporation (CNOOC) has announced the discovery of a major billion-ton oil and gas field in the shallow waters of the Bohai Sea — the Qinhuangdao 29-6 oilfield. This marks the seventh consecutive billion-ton oil and gas field identified since 2019 within the Bohai oilfield, China's largest crude oil production base.

Located in the central Bohai Sea, approximately 44 kilometres west of Jingtang Port, the Qinhuangdao 29-6 oilfield represents another significant billion-tonne lithological oil discovery, following the Qinhuangdao 27-3 field in recent years. The discovery well encountered 66.7 metres of oil-bearing strata and reached a total drilling depth of 1,688 metres. Test results indicate that a single well can produce around 370 tonnes of crude oil per day, highlighting favourable exploration potential.

The newly discovered field lies within the slope zone at the margin of the Shijoutuo uplift in the Bohai Bay Basin. The Shijoutuo uplift was among the earliest key exploration targets during the development of the Bohai oilfields. Metaphorically, if the uplift is considered a mountain, the Qinhuangdao 29-6 oilfield is situated at its base. Conventional exploration theory holds that uplift slope zones mainly act as migration pathways for hydrocarbons moving from source rocks to higher structural positions. Due to the lack of effective fault-related traps, hydrocarbons are often thought to migrate through these zones without accumulating, limiting the formation of large-scale reservoirs. As a result, multiple stages of exploration in the Shijoutuo uplift slope zone since the 1970s have yielded limited results.

In 2024, however, the discovery of the Qinhuangdao 27-3 billion-tonne lithological oilfield within the Shijoutuo uplift provided important technical experience and conceptual breakthroughs. By integrating extensive well data with experimental analyses, CNOOC researchers identified numerous microscopic and previously 'invisible' lithological traps along hydrocarbon migration pathways, confirming the uplift slope zone's capacity to store hydrocarbons. Building on this understanding, researchers combined sedimentological and geochemical studies to delineate hydrocarbon-enriched areas. Targeted drilling was subsequently implemented, leading to the successful discovery of the Qinhuangdao 29-6 billion-tonne lithological oilfield, characterised by its low-lying, marginal, and inclined structural setting.

A CNOOC representative noted that improved insights into oil and gas migration and accumulation patterns in Neogene shallow slope zones, together with ongoing technological innovation, were key to the breakthrough. The discovery challenges the traditional view that slope zones function solely as hydrocarbon conduits, demonstrating the substantial exploration potential of uplift slope areas under conditions of strong extensional and strike-slip fault activity.

The Qinhuangdao 29-6 oilfield is the second billion-tonne lithological oilfield discovered in the Shijoutuo uplift exploration area of the Bohai Bay Basin. The finding further highlights the value of refined geological understanding and detailed exploration, strengthening China's resource base for reserve growth and production increases. It is of considerable significance for ensuring stable energy supplies and supporting the coordinated development of the Beijing–Tianjin–Hebei region.