New fields, new types and resource potentials of oil-gas exploration in Bohai Sea

Since more than 60 year exploration and development, the Bohai oilfield has now been a super large offshore oilfield in China. This paper reviews the exploration progresses of Bohai oilfield since the 13th Five Year Plan(2016-2020), and clearly points out the key exploration fields and research directions in future based on the analysis of regional accumulation conditions. The Bohai Sea area mainly develops three sets of main source strata, i. e., Member 3 of Shahejie Formation, Member 1 of Shahejie Formation, and Member 3 of Dongying Formation. Vertically, the Cenozoic clastic reservoirs and buried-hill fractured reservoirs constitute the main productive series. Based on recognition of the special geological conditions of Bohai Sea, such as "intense Mesozoic destruction, rapid Paleogene transformation, and thick Neogene sedimentation", the paper establishes and developes multiple new petroleum geological understandings of the three major exploration fields in Bohai oilfield, including "complex metamorphic buried-hills", "Paleogene structure-lithology", and "large-scale Neogene lithology", which has achieved significant discoveries of five oilfields of 100 million tons in five years. Through the systematic analysis of source rocks, reservoir cap association, and other regional accumulation conditions in the basin, it is specified that the main potential areas for future conventional exploration fields are the buried-hill field including Liaonan belt, Liaobei belt and circum-Bozhong sag, the Palaeogene field including Liaozhong-Liaoxibei subsag belt, Shinan steep-slope belt, Bozhong southwest area and north steep-slope belt of Huanghekou sag, and the shallow Neogene field in circum-Bozhong sag. For unconventional oil-gas field, shale oil in Laizhouwan sag should be prioritized. The crude oil and natural gas in the above-mentioned conventional hydrocarbon traps are approximately estimated to be 8.7×108 t, and 1.9×1012 m3, respectively; the unconventional shale oil resource amounts to nearly 8.6×108 t in Laizhouwan sag. It is pointed out that the future oil-gas exploration in Bohai Sea needs to realize four shifts, i. e., the shift of buried hill exploration from traditional buried-hills to hidden buried-hills, the shift of Paleogene exploration from medium-deep to deep and ultra-deep strata, the shift of shallow lithology exploration from salients and slopes to sags, and the shift of exploration fields from conventional to both conventional and unconventional oil-gas. The research results can contribute to the advancement of oil-gas geological theory and technology in complex continental downfaulted basins, providing theoretical understanding and support for the stable and sustainable development of Bohai oilfield. © 2024 Science Press. All rights reserved.